U.S. patent application number 12/374477 was filed with the patent office on 2009-12-24 for method of dopant injection, n-type silicon single-crystal, doping apparatus and pull-up device.
Invention is credited to Shinichi Kawazoe, Toshimichi Kubota, Yasuhito Narushima.
Application Number | 20090314996 12/374477 |
Document ID | / |
Family ID | 38956908 |
Filed Date | 2009-12-24 |
United States Patent
Application |
20090314996 |
Kind Code |
A1 |
Kawazoe; Shinichi ; et
al. |
December 24, 2009 |
METHOD OF DOPANT INJECTION, N-TYPE SILICON SINGLE-CRYSTAL, DOPING
APPARATUS AND PULL-UP DEVICE
Abstract
In a dopant-injecting method for injecting a volatile dopant
into a semiconductor melt, a doping device having an accommodating
portion for accommodating a solid dopant and a cylindrical portion
into which a gas ejected from the accommodating portion is
introduced, a lower end surface of the cylindrical portion being
opened to guide the gas to the melt, is used. The sublimation rate
of the dopant in the accommodating portion is set in a range from
10 g/min to 50 g/min. Since a flow volume of the volatilized dopant
gas is controlled by setting the sublimation rate of the dopant gas
in the accommodating portion in the range from 10 g/min to 50
g/min, the melt is not blown off when the gas is blown onto the
melt.
Inventors: |
Kawazoe; Shinichi;
(Nagasaki, JP) ; Narushima; Yasuhito; (Nagasaki,
JP) ; Kubota; Toshimichi; (Nagasaki, JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN & CHICK, PC
220 Fifth Avenue, 16TH Floor
NEW YORK
NY
10001-7708
US
|
Family ID: |
38956908 |
Appl. No.: |
12/374477 |
Filed: |
July 20, 2007 |
PCT Filed: |
July 20, 2007 |
PCT NO: |
PCT/JP2007/064362 |
371 Date: |
January 20, 2009 |
Current U.S.
Class: |
252/500 ;
118/715; 257/E21.482; 438/510 |
Current CPC
Class: |
C30B 15/04 20130101;
C30B 29/06 20130101 |
Class at
Publication: |
252/500 ;
438/510; 118/715; 257/E21.482 |
International
Class: |
H01B 1/04 20060101
H01B001/04; H01L 21/46 20060101 H01L021/46 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 20, 2006 |
JP |
2006-198669 |
Jul 20, 2006 |
JP |
2006-198670 |
Sep 29, 2006 |
JP |
2006-267264 |
Claims
1. A dopant-injecting method for injecting a volatile dopant into a
semiconductor melt, comprising: providing a doping device including
an accommodating portion that accommodates a solid dopant and a
cylindrical portion into which a gas ejected from the accommodating
portion is introduced, the cylindrical portion having an opening on
a lower end surface to guide the gas to the melt; and setting a
sublimation rate of the dopant in the accommodating portion in a
range from 10 g/min to 50 g/min.
2. The dopant-injecting method according to claim 1, wherein: the
semiconductor melt is a silicon melt; the doping device is provided
with a blow-preventing member above the accommodating portion, the
blow-preventing member preventing an inert gas flowing from above
to below the accommodating portion from being directly blown to the
accommodating portion, the doping device being disposed in a
chamber of a pull-up device accommodating a crucible containing the
melt; and when the dopant is injected, following conditions (A) to
(C) are satisfied: (A) a temperature of the melt is in a range from
a melting point of silicon and a point 60.degree. C. above the
melting point; (B) a flow volume of the inert gas flowing from
above to below the accommodating portion of the doping device is in
a range from 50 litters/min to 400 litters/min; and (C) a pressure
inside the chamber is set in a range from 5332 Pa (converted value
of 40 Torr) to 79980 Pa (converted value of 600 Torr).
3. The dopant-injecting method according to claim 1, wherein: the
semiconductor melt is a silicon melt; the doping device is provided
with a blow-preventing member above the accommodating portion, the
blow-preventing member preventing an inert gas flowing from above
to below the accommodating portion from being directly blown to the
accommodating portion, the doping device being disposed in a
chamber of a pull-up device accommodating a crucible containing the
melt; and when the dopant is injected, following conditions (D) to
(F) are satisfied: (D) a temperature of the melt is in a range from
a melting point of silicon and a point 60.degree. C. above the
melting point; (E) a flow volume of the inert gas flowing from
above to below the accommodating portion of the doping device is in
a range from 50 litters/min to 400 litters/min; and (F) a flow rate
of the inert gas at an entrance of the chamber is in a range from
0.05 m/s to 0.2 m/s.
4. The dopant-injecting method according to claim 1, wherein: a
diameter of the opening of the cylindrical portion is 20 mm or
more.
5. The dopant-injecting method according to claim 1, wherein: the
dopant accommodated in the accommodating portion of the doping
device is located higher than a surface of the melt by 300 mm or
more.
6. The dopant-injecting method according to claim 1, wherein: the
dopant gas is injected while a part of the melt on which the dopant
gas is blown is being stirred.
7. The dopant-injecting method according to claim 1, wherein: the
doping device includes a plurality of heat-shielding members that
cover a lower side of the accommodating portion to block a radiant
heat from the melt, and the dopant is injected with a position and
a number of the plurality of heat-shielding members being
adjusted.
8. A dopant-injecting method for injecting volatilized dopant gas
into a semiconductor melt, comprising: injecting the dopant gas
while a part of the melt on which the dopant gas is blown is being
stirred.
9. The dopant-injecting method according to claim 8, wherein: a
doping device including an accommodating portion that accommodates
a solid dopant and a tube portion into which the gas ejected from
the accommodating portion is introduced is used, the tube portion
having an open lower end surface and a lower end immersed in the
melt; a through-hole is provided on the tube portion of the doping
device at a portion immersed in the melt, and the melt is
introduced into an interior of the tube portion through the
through-hole or is ejected from the interior of the tube through
the through-hole when at least one of the doping device and a
crucible containing the melt is driven to stir the portion of the
melt on which the dopant gas is blown.
10. The dopant-injecting method according to claim 9, wherein: a
vane that protrudes outward from the tube portion and has a vane
surface extending along an axis of the tube portion is provided on
the portion of the tube portion of the doping device immersed in
the melt adjacent to the through-hole, and the melt is blocked by
the vane surface of the vane when the at least one of the doping
device and the crucible is rotated to guide the melt into the
interior of the tube portion through the through-hole.
11. An N-type silicon monocrystal with a resistivity of 3
m.OMEGA.cm or less, the N-type silicon monocrystal being
manufactured by the dopant-injecting method according to claim
1.
12. A doping device used for injecting a volatile dopant into a
semiconductor melt, the device comprising: an accommodating portion
that accommodates a solid dopant; a blow-preventing member provided
above the accommodating portion, the blow-preventing member
preventing an inert gas flowing from above to below the
accommodating portion from being directly blown to the
accommodating portion; a cylindrical portion having openings on
upper and lower end surfaces thereof, the opening on the upper end
surface being in communication with the accommodating portion to
guide a volatilized dopant gas to the melt; and a heat-shielding
member at least covering a lower side of the accommodating portion
to block a radiant heat from the melt to the accommodating
portion.
13. The doping device according to claim 12, further comprising: an
inner tube provided with the accommodating portion and the
cylindrical portion; and an outer tube that accommodates the inner
tube and has an opening on a lower end surface thereof, an upper
portion opposite to the opening and a cylindrical lateral portion
extending from a periphery of the upper portion toward the melt,
wherein the upper portion of the outer tube provides the
blow-preventing member, and the heat-shielding member is arranged
to shield a space between the cylindrical portion of the inner tube
and an inner circumference of the lateral portion of the outer
tube.
14. The doping device according to claim 13, wherein: a lower end
of the lateral portion of the outer tube protrudes toward the melt
relative to a lower end of the cylindrical portion of the inner
tube.
15. The doping device according to claim 14, wherein: a path for
re-introducing a part of the dopant gas blown from the lower end of
the inner tube to the surface of the melt without being dissolved
therein to the surface of the melt is provided between the
cylindrical portion of the inner tube and the outer tube.
16. The doping device according to claim 13, wherein: the
heat-shielding member is provided with a plurality of
heat-shielding plates that are arranged to shield a space between
an outer circumference of the cylindrical portion of the inner tube
and an inner circumference of the lateral portion of the outer
tube, a first heat-shielding plate of the plurality of
heat-shielding plates closest to the accommodating portion of the
inner tube is made of opaque quartz, and a second heat-shielding
plate closest to the melt is made of a graphite member.
17. A doping device used for injecting a volatilized dopant gas
into a semiconductor melt, the device comprising: an accommodating
portion that accommodates a solid dopant; a tube portion in which a
gas ejected from the accommodating portion is introduced, the tube
portion having an opening on a lower end surface, a lower end of
the tube portion being immersed in the melt; and a through-hole
provided on the tube portion at a portion immersed in the melt.
18. The doping device according to claim 17, further comprising: a
vane that protrudes outward from the tube portion and has a vane
surface extending along an axis of the tube portion, the vane being
provided on the portion of the tube portion immersed in the melt
adjacent to the through-hole.
19. The doping device according to claim 17, further comprising: an
inner tube including the accommodating portion and a cylindrical
portion having an opening on upper and lower ends thereof, the
accommodating portion being in communication with the upper end of
the cylindrical portion to guide the volatilized dopant gas to the
melt, the cylindrical portion not touching the melt, wherein the
tube portion is a cylindrical outer tube accommodating the inner
tube and having a lower end protruding toward the melt relative to
a lower end of the cylindrical portion.
20. A pull-up device, comprising: the doping device according to
claim 12; a crucible containing a melt; and a heat shielding shield
covering a surface of the melt in the crucible and surrounding the
doping device.
Description
TECHNICAL FIELD
[0001] The present invention relates to an injecting method of
dopant, an N-type silicon monocrystal, a doping device and a
pull-up device.
BACKGROUND ART
[0002] Traditionally, in order to adjust resistance value of
semiconductor silicon wafers, microelements (dopants) such as
phosphorous and arsenic are doped while developing N-type silicon
monocrystals.
[0003] The doping on silicon monocrystals produced by Czochralski
method is conducted by blowing a gas in which the microelements are
volatilized onto silicon melt (see e.g. Patent Document 1) or by
directly adding solid microelements into silicon melt (see e.g.
Patent Document 2).
[0004] In order to blow the microelement gas to silicon melt, solid
microelement is initially housed in an accommodating portion of a
doping device. Then, the solid microelement is vaporized in a
high-temperature atmosphere in a chamber of a pull-up device, thus
blowing the microelement gas to the surface of the silicon
melt.
[0005] Alternatively, in order to directly add a solid microelement
into silicon melt, the solid microelement is put into an injection
tube (doping device) having sealed upper and lateral portions and a
latticed (netted) lower portion. The lower portion of the injection
tube is immersed in the silicon melt to vaporize the microelement
by the temperature of the silicon melt.
[0006] Patent Document 1: JP-A-2001-342094 (P. 3-6, FIGS. 1, 2)
[0007] Patent Document 2: JP-A-2004-137140 (P. 5-7, FIG. 4)
DISCLOSURE OF THE INVENTION
Problems to Be Solved by the Invention
[0008] However, according to the above first method, since the
microelement gas is blown only to the same part on the surface of
the silicon melt, it is difficult for the gas to be dissolved into
the silicon melt, or the gas is discharged out of the furnace
without touching the silicon melt. On the other hand, when the
solid dopant is vaporized by the heat of the silicon melt to blow
the dopant gas to the silicon melt, since the atmospheric
temperature of the silicon melt is much higher than sublimation
temperature of the dopant, the dopant is instantaneously
sublimated. Accordingly, the pressure within the storage is greatly
increased relative to the outside of the storage, so that the
dopant gas is vigorously blown to the silicon melt.
[0009] Further, when the dopant is rapidly sublimated, since the
blowing pressure of the dopant gas becomes excessively high, the
dopant gas outbursts too fast to be dissolved in the melt, so that
only a tiny fraction of the added dopant is dissolved into the
melt, thereby deteriorating absorption rate.
[0010] Further, since the silicon melt is blown off by the dopant
gas, the blown-off fraction of silicon hinders the formation of
monocrystal to make it difficult to manufacture a semiconductor
wafer having a desired resistance value.
[0011] Furthermore, in any of the above dopant-injecting methods,
it is difficult to manufacture a semiconductor wafer having a
desired resistance value.
[0012] An object of the present invention is to provide an
injecting method of dopant capable of manufacturing a semiconductor
wafer having a desired resistance value, and an N-type silicon
monocrystal manufactured by the dopant injecting method.
[0013] Another object of the invention is to provide a
dopant-injecting method and a doping device capable of enhancing a
doping efficiency of a dopant into a silicon melt.
[0014] Still another object of the invention is to provide a doping
device capable of manufacturing a semiconductor wafer having a
desired resistance value and a pull-up device having the doping
device.
Means for Solving the Problems
[0015] After vigorous research of the inventors of the invention,
it was estimated that, since the heat of the silicon melt is
enormously large relative to a sublimation rate of microelement,
the microelement is rapidly sublimated to blow an intensive jet of
the microelement gas onto the silicon melt in the above-described
dopant-injecting method. Since an extremely large amount of
microelement gas is blown, blowing pressure of the dopant gas
becomes excessively high, so that the dopant gas outbursts too
rapidly to be dissolved in the melt, so that only a tiny fraction
of the added dopant is dissolved into the melt, thereby
deteriorating absorption rate. Further, the formation of
monocrystal is hindered by the blown-off silicon to make it
difficult to manufacture semiconductor wafers having a desired
resistance value.
[0016] The present invention has been devised on the basis of
knowledge as described above.
[0017] A dopant-injecting method according to an aspect of the
invention is for injecting a volatile dopant into a semiconductor
melt, which includes: providing a doping device including an
accommodating portion that accommodates a solid dopant and a
cylindrical portion into which a gas ejected from the accommodating
portion is introduced, the cylindrical portion having an opening on
a lower end surface to guide the gas to the melt; and setting a
sublimation rate of the dopant in the accommodating portion in a
range from 10 g/min to 50 g/min.
[0018] In the invention, the melt may be doped with the cylindrical
portion of the doping device being immersed in the melt.
Alternatively, the melt may be doped without immersing the
cylindrical portion in the melt.
[0019] According to the above aspect of the invention, since a flow
volume of the volatilized dopant gas is controlled by setting the
sublimation rate of the dopant gas in the accommodating portion in
the range from 10 g/min to 50 g/min, the melt is not blown off when
the gas is blown onto the melt.
[0020] Further, since it can be prevented that time allowance for
dissolving the dopant into the melt is lost on account of
excessively ejected dopant gas, the dopant can be sufficiently
dissolved into the melt, so that absorption rate is not
deteriorated. Further, it can be prevented that the formation of
monocrystal is hindered by the blown-off silicon to make it
difficult to manufacture semiconductor wafers having a desired
resistance value.
[0021] In the above aspect of the invention, it is preferable that
the semiconductor melt is a silicon melt; the doping device is
provided with a blow-preventing member above the accommodating
portion, the blow-preventing member preventing an inert gas flowing
from above to below the accommodating portion from being directly
blown to the accommodating portion, the doping device being
disposed in a chamber of a pull-up device accommodating a crucible
containing the melt; and when the dopant is injected, following
conditions (A) to (C) are satisfied: (A) a temperature of the melt
is in a range from a melting point of silicon and a point
60.degree. C. above the melting point; (B) a flow volume of the
inert gas flowing from above to below the accommodating portion of
the doping device is in a range from 50 litters/min to 400
litters/min; and (C) a pressure inside the chamber is set in a
range from 5332 Pa (converted value of 40 Torr) to 79980 Pa
(converted value of 600 Torr).
[0022] When the temperature of the melt is lower than the melting
point of silicon, the dopant gas absorption may be hindered. On the
other hand, when the melt temperature exceeds the point 60.degree.
C. above the melting point, the melt may be boiled. Further,
evaporation of dopant gas absorbed in the melt may be promoted to
deteriorate the absorption rate of the dopant.
[0023] When the pressure inside the chamber is 5332 Pa (converted
value of 40 Torr), the dopant dissolved in the melt may be easily
volatilized.
[0024] On the other hand, when the pressure inside the chamber
exceeds 79980 Pa (converted value of 600 Torr), high pressure
resistance and heat resistance are required for the chamber, which
incurs additional production cost.
[0025] The flow volume of the inert gas flowing from above to below
the accommodating portion of the doping device is in a range from
50 litters/min to 400 litters/min. Accordingly, the accommodating
portion can be cooled by the inert gas, thus allowing adjustment of
the sublimation rate of the dopant in the accommodating
portion.
[0026] When the flow volume of the inert gas is set to exceed 400
litters/min, the accommodating portion may be too cooled to
volatilize the dopant.
[0027] In the above aspect of the invention, it is preferable that
the semiconductor melt is a silicon melt; the doping device is
provided with a blow-preventing member above the accommodating
portion, the blow-preventing member preventing an inert gas flowing
from above to below the accommodating portion from being directly
blown to the accommodating portion, the doping device being
disposed in a chamber of a pull-up device accommodating a crucible
containing the melt; and when the dopant is injected, following
conditions (D) to (F) are satisfied: (D) a temperature of the melt
is in a range from a melting point of silicon and a point
60.degree. C. above the melting point; (E) a flow volume of the
inert gas flowing from above to below the accommodating portion of
the doping device is in a range from 50 litters/min to 400
litters/min; and (F) a flow rate of the inert gas at an entrance of
the chamber is in a range from 0.05 m/s to 0.2 m/s.
[0028] The entrance of chamber refers to a border area between the
chamber and a pulling-up chamber.
[0029] According to the above arrangement, since the sublimation
rate of the dopant can be set within an appropriate range by
controlling the flow rate at the entrance of the chamber, the melt
is not blown off.
[0030] In the above aspect of the invention, it is preferable that
a diameter of the opening of the cylindrical portion is 20 mm or
more.
[0031] Since the diameter of the opening of the cylindrical
portion, i.e. the ejecting opening of the gas, is 20 mm or more,
when the sublimation rate of the dopant in the accommodating
portion is set in the range from 10 g/min to 50 g/min, the
volatilized dopant gas is not vigorously blown onto the melt, so
that blow-off of the melt can be reliably avoided.
[0032] Further, in the above aspect of the invention, the dopant
accommodated in the accommodating portion of the doping device is
located higher than a surface of the melt by 300 mm or more.
[0033] If the position of the dopant is located very close to the
surface of the melt when being doped, the dopant is disposed in a
high temperature atmosphere due to the heat of the melt, so that it
may become difficult to control the sublimation rate of the
dopant.
[0034] In this arrangement, since the position of the dopant is
located 300 mm or more above the surface of the melt, the
sublimation rate of the dopant can be reliably controlled.
[0035] In the above aspect of the invention, it is preferable that
the dopant gas is injected while a part of the melt on which the
dopant gas is blown is being stirred.
[0036] According to the above arrangement, since the dopant gas is
injected while stirring the part of the melt on which the dopant
gas is blown, the melt being in contact with the gas does not stay
the same but is constantly renewed. Accordingly, the gas can be
efficiently brought into contact with the melt into which the gas
is dissolved, so that the doping efficiency can be enhanced.
[0037] In the above aspect of the invention, it is preferable that
the doping device includes a plurality of heat-shielding members
that cover a lower side of the accommodating portion to block a
radiant heat from the melt, and the dopant is injected with a
position and a number of the plurality of heat-shielding members
being adjusted.
[0038] According to the above arrangement, since the sublimation
rate of the dopant in the accommodating portion can be adjusted by
adjusting the position and the number of the heat-shielding
members, the sublimation rate of the dopant can be set as
desired.
[0039] In the dopant-injecting method according to the above aspect
of the invention, it is preferable that a doping device including
an accommodating portion that accommodates a solid dopant and a
tube portion into which the gas ejected from the accommodating
portion is introduced is used, the tube portion having an open
lower end surface and a lower end immersed in the melt; a
through-hole is provided on the tube portion of the doping device
at a portion immersed in the melt, and the melt is introduced into
an interior of the tube portion through the through-hole or is
ejected from the interior of the tube through the through-hole when
at least one of the doping device and a crucible containing the
melt is driven to stir the portion of the melt on which the dopant
gas is blown.
[0040] With the use of the above doping device, since the outer
tube protruding toward the melt relative to the inner tube of the
doping device is provided, the gas ejected from the cylindrical
portion of the inner tube is introduced to the outer tube. Since
the through-hole is provided on the outer tube and the melt is
introduced into the interior of the outer tube or is ejected from
the interior of the outer tube through the through-hole when the
doping device and/or the crucible containing the melt is driven,
the melt inside the cylindrical portion, i.e. the melt in contact
with the gas, is exchanged by the stirring.
[0041] Accordingly, it is facilitated for the gas in the outer tube
to be dissolved in the melt, so that the doping efficiency can be
enhanced.
[0042] A dopant-injecting method according to another aspect of the
invention is for injecting volatilized dopant gas into a
semiconductor melt, the method including: injecting the dopant gas
while a part of the melt on which the dopant gas is blown is being
stirred.
[0043] According to the above arrangement, since the dopant gas is
injected while stirring the part of the melt on which the dopant
gas is blown, the melt being in contact with the gas does not stay
the same but is constantly renewed. Accordingly, the dopant gas can
be efficiently brought into contact with the melt in which the gas
is not dissolved, so that the doping efficiency can be
enhanced.
[0044] In the above aspect of the invention, it is preferable that
a doping device including an accommodating portion that
accommodates a solid dopant and a tube portion into which the gas
ejected from the accommodating portion is introduced is used, the
tube portion having an open lower end surface and a lower end
immersed in the melt; a through-hole is provided on the tube
portion of the doping device at a portion immersed in the melt, and
the melt is introduced into an interior of the tube portion through
the through-hole or is ejected from the interior of the tube
through the through-hole when at least one of the doping device and
a crucible containing the melt is driven to stir the portion of the
melt on which the dopant gas is blown.
[0045] According to the above arrangement, since the through-hole
is provided on the tube portion into which the gas ejected from the
accommodating portion of the doping device is introduced is
provided and the melt is introduced into the interior of the tube
portion or is ejected from the interior of the tube portion through
the through-hole when the doping device and/or the crucible
containing the melt is driven, the melt inside the tube portion,
i.e. the melt in contact with the gas, is exchanged by the
stirring.
[0046] Accordingly, it is facilitated for the gas in the tube
portion to be dissolved in the melt, so that the doping efficiency
can be enhanced.
[0047] Further, since it can be prevented that time allowance for
dissolving the dopant into the melt is lost on account of
excessively ejected dopant gas, the dopant can be sufficiently
dissolved into the melt, so that absorption rate is not
deteriorated. Further, it can be prevented that the formation of
monocrystal is hindered by the blown-off silicon to make it
difficult to manufacture semiconductor wafers having a desired
resistance value.
[0048] In the above aspect of the invention, it is preferable that
a vane that protrudes outward from the tube portion and has a vane
surface extending along an axis of the tube portion is provided on
the portion of the tube portion of the doping device immersed in
the melt adjacent to the through-hole, and the melt is blocked by
the vane surface of the vane when the at least one of the doping
device and the crucible is rotated to guide the melt into the
interior of the tube portion through the through-hole.
[0049] When the crucible is rotated while fixing the doping device,
the vane is preferably provided adjacent to a forward end of the
through-hole in the rotary direction of the crucible.
[0050] When the doping device is rotated, the vane is preferably
provided adjacent to a rear end of the through-hole in the rotary
direction of the crucible.
[0051] According to the above arrangement, since the vane having
the vane surface extending along the axis of the tube portion is
provided at the portion of the tube portion of the doping device
adjacent to the through-hole, the melt is blocked by the vane
surface of the vane to be introduced to the interior of the tube
portion through the through-hole when at least one of the tube
portion of the doping device and the crucible containing the melt
is rotated.
[0052] Since the melt to be in contact with the dopant gas can be
stirred merely by rotating one of the tube portion of the doping
device and the crucible containing the melt, the doping process can
be facilitated.
[0053] An N-type silicon monocrystal according to still another
aspect of the invention has a resistivity of 3 m.OMEGA.cm or less,
the N-type silicon monocrystal being manufactured by the
dopant-injecting method according to one of the above aspects of
the invention.
[0054] According to the above aspect of the invention, the
above-described dopant-injecting method used for producing silicon
monocrystal allows stable production of a low resistivity silicon
monocrystal (N-type silicon monocrystal having resistivity of 3
m.OMEGA.cm or below).
[0055] A doping device according to further aspect of the invention
is used for injecting a volatile dopant into a semiconductor melt,
the device including: an accommodating portion that accommodates a
solid dopant; a blow-preventing member provided above the
accommodating portion, the blow-preventing member preventing an
inert gas flowing from above to below the accommodating portion
from being directly blown to the accommodating portion; a
cylindrical portion having openings on upper and lower end surfaces
thereof, the opening on the upper end surface being in
communication with the accommodating portion to guide a volatilized
dopant gas to the melt; and a heat-shielding member at least
covering a lower side of the accommodating portion to block a
radiant heat from the melt to the accommodating portion.
[0056] When the melt is doped using the doping device of the above
aspect of the invention, the volatile dopant may be injected into
the melt while immersing the lower end of the cylindrical portion
into the silicon melt. Alternatively, the dopant may be injected
into the melt by blowing the volatilized dopant gas onto the melt
with the lower end of the cylindrical portion being spaced apart
from the silicon melt.
[0057] According to the above aspect of the invention, since the
heat-shielding member that covers at least the lower side of the
accommodating portion in which the dopant is accommodated to block
the radiant heat from the melt to the accommodating portion is
provided, the radiant heat of the melt is not easily transferred to
the lower side of the accommodating portion. Accordingly, the
volatilization rate of the dopant in the accommodating portion can
be lowered as compared to the volatilization rate of a traditional
doping device. Thus, the blowing pressure of the dopant gas to the
melt can be lowered. Consequently, the silicon melt blown off by
the gas can be reduced.
[0058] Accordingly, since it can be prevented that time allowance
for dissolving the dopant into the melt is lost on account of
excessively ejected dopant gas, the dopant can be sufficiently
dissolved into the melt, so that absorption rate is not
deteriorated. Further, it can be prevented that the formation of
monocrystal is hindered by the blown-off silicon to make it
difficult to manufacture semiconductor wafers having a desired
resistance value.
[0059] The doping device of the above aspect of the invention is
provided with the cylindrical portion having the opening on the
upper end in communication with the accommodating portion to guide
the volatilized dopant gas to the melt. Since the cylindrical
portion is provided to form the path for guiding the volatilized
dopant gas to the melt, the doping efficiency to the melt can be
enhanced.
[0060] Inert gas such as argon gas is flowed in the pull-up device
from above to below the accommodating portion. Since the doping
device of the above aspect of the invention is provided with the
blow-preventing member for preventing the gas from being directly
blown to the accommodating portion, the temperature of the
accommodating portion is not excessively cooled by the blown gas to
become lower than an evaporation temperature of the dopant.
[0061] In the above aspect of the invention, it is preferable that
an inner tube provided with the accommodating portion and the
cylindrical portion; and an outer tube that accommodates the inner
tube and has an opening on a lower end surface thereof, an upper
portion opposite to the opening and a cylindrical lateral portion
extending from a periphery of the upper portion toward the melt,
where the upper portion of the outer tube provides the
blow-preventing member, and the heat-shielding member is arranged
to shield a space between the cylindrical portion of the inner tube
and an inner circumference of the lateral portion of the outer
tube.
[0062] According to the above arrangement, since the doping device
includes the outer tube that accommodates the inner tube having the
accommodating portion and the cylindrical portion, it can be
assured that the inert gas such as argon gas is not directly blown
to the inner tube.
[0063] In the above aspect of the invention, it is preferable that
a lower end of the lateral portion of the outer tube protrudes
toward the melt relative to a lower end of the cylindrical portion
of the inner tube.
[0064] Since the lower end of the outer tube is protruded toward
the melt relative to the lower end of the cylindrical portion of
the inner tube, the doping process can be conducted while immersing
only the lower end of the outer tube.
[0065] With this arrangement, even when a part of the gas ejected
from the cylindrical portion of the inner tube is not dissolved
into the melt, the gas resides within a space defined by the
cylindrical portion of the inner tube, the outer tube and the
heat-shielding member without being ejected outside the doping
device, so that the doping efficiency can be enhanced.
[0066] Further, since only the lower end of the outer tube can be
immersed in the melt without immersing the lower end of the
cylindrical portion of the inner tube, the heat of the melt is not
directly transferred to the inner tube. Accordingly, the
temperature of the accommodating portion is not raised on account
of direct transmission of the heat of the melt to the inner tube,
so that increase in the volatilization rate of the dopant in the
accommodating portion can be prevented.
[0067] In the above aspect of the invention, it is preferable that
a path for re-introducing a part of the dopant gas blown from the
lower end of the inner tube to the surface of the melt without
being dissolved therein to the surface of the melt is provided
between the cylindrical portion of the inner tube and the outer
tube.
[0068] According to the above arrangement, since a path for
re-introducing a part of the dopant gas blown from the lower end of
the inner tube without touching the melt surface toward the surface
of the melt is provided between the cylindrical portion of the
inner tube and the outer tube, the doping efficiency can be
enhanced.
[0069] In the above aspect of the invention, it is preferable that
the heat-shielding member is provided with a plurality of
heat-shielding plates that are arranged to shield a space between
an outer circumference of the cylindrical portion of the inner tube
and an inner circumference of the lateral portion of the outer
tube, a first heat-shielding plate of the plurality of
heat-shielding plates closest to the accommodating portion of the
inner tube is made of opaque quartz, and a second heat-shielding
plate closest to the melt is made of a graphite member.
[0070] According to the above arrangement, since the heat-shielding
plate closest to the accommodating portion of the inner tube of the
doping device is made of opaque quartz with high heat conductivity,
the heat is not accumulated in the heat-shielding plate closest to
the accommodating portion. Accordingly, since the accommodating
portion is not heated by the heat accumulated in the heat-shielding
plate, the volatilization rate of the dopant in the accommodating
portion is not accelerated by the presence of the heat-shielding
plate.
[0071] Further, since the heat-shielding plate closest to the melt
is made of a material having relatively low heat conductivity such
as graphite, the heat transmission from the melt can be blocked at
a position remote from the accommodating portion, which also
contributes to prevention of increase in the volatilization rate of
the dopant in the accommodating portion.
[0072] A doping device according to still further aspect of the
invention is used for injecting a volatilized dopant gas into a
semiconductor melt, the device including: an accommodating portion
that accommodates a solid dopant; a tube portion in which a gas
ejected from the accommodating portion is introduced, the tube
portion having an opening on a lower end surface, a lower end of
the tube portion being immersed in the melt; and a through-hole
provided on the tube portion at a portion immersed in the melt.
[0073] According to the above arrangement, since the through-hole
is provided on the tube portion into which the gas ejected from the
accommodating portion of the doping device is introduced, the melt
is introduced into the interior of the tube portion or is ejected
from the interior of the tube portion through the through-hole to
be stirred when at least one of the doping device and the crucible
containing the melt is driven. Accordingly, the melt inside the
tube portion (i.e. the melt in contact with the gas) is exchanged
by the stirring.
[0074] Consequently, it is facilitated for the gas in the tube
portion to be dissolved in the melt, so that the doping efficiency
can be enhanced.
[0075] In the above aspect of the invention, it is preferable that
a vane that protrudes outward from the tube portion and has a vane
surface extending along an axis of the tube portion, the vane being
provided on the portion of the tube portion immersed in the melt
adjacent to the through-hole.
[0076] According to the above arrangement, since the vane having
the vane surface extending along the axis of the tube portion is
provided at the portion of the tube portion of the doping device
adjacent to the through-hole, the melt is blocked by the vane
surface of the vane to be introduced to the interior of the tube
portion through the through-hole when at least one of the tube
portion of the doping device and the crucible containing the melt
is rotated.
[0077] Since the melt to be in contact with the dopant gas can be
stirred merely by rotating one of the tube portion of the doping
device and the crucible containing the melt, the doping process can
be facilitated.
[0078] In the above aspect of the invention, it is preferable that
an inner tube including the accommodating portion and a cylindrical
portion having an opening on upper and lower ends thereof, the
accommodating portion being in communication with the upper end of
the cylindrical portion to guide the volatilized dopant gas to the
melt, the cylindrical portion not touching the melt, in which the
tube portion is a cylindrical outer tube accommodating the inner
tube and having a lower end protruding toward the melt relative to
a lower end of the cylindrical portion.
[0079] With the above arrangement, since the lower end of the outer
tube is protruded toward the melt relative to the lower end of the
cylindrical portion of the inner tube, the doping process can be
conducted while immersing only the lower end of the outer tube.
[0080] Since only the lower end of the outer tube can be immersed
in the melt without immersing the lower end of the cylindrical
portion of the inner tube, the heat of the melt is not directly
transferred to the inner tube. Accordingly, the temperature of the
accommodating portion is not raised on account of direct
transmission of the heat of the melt to the inner tube, so that
abrupt increase in the volatilization rate of the dopant
accommodated in the accommodating portion can be prevented.
[0081] A pull-up device according to still further aspect of the
invention includes: the doping device according to the above aspect
of the invention; a crucible containing a melt; and a heat
shielding shield covering a surface of the melt in the crucible and
surrounding the doping device.
[0082] With the pull-up device, since the above-described doping
device is provided, a semiconductor wafer having a desired
resistance value can be produced.
BRIEF DESCRIPTION OF DRAWINGS
[0083] FIG. 1 is a cross-sectional view showing a pull-up device
according to a first and fifth exemplary embodiments of the
invention.
[0084] FIG. 2 is a cross-sectional view showing a doping device of
the pull-up device.
[0085] FIG. 3 is a cross-sectional view showing a pull-up device
according to a second exemplary embodiment of the invention.
[0086] FIG. 4 is a cross-sectional view showing a doping device of
the second exemplary embodiment.
[0087] FIG. 5 is a schematic view showing a doping process using
the doping device of the second exemplary embodiment.
[0088] FIG. 6 is a cross-sectional view showing a doping device of
a third exemplary embodiment of the invention.
[0089] FIG. 7 is a cross-sectional view showing a doping device
according to a modification of the first to third exemplary
embodiments and the fifth exemplary embodiment.
[0090] FIG. 8 is a cross-sectional view showing a doping device
according to another modification of the first to third exemplary
embodiments.
[0091] FIG. 9 is a cross-sectional view showing a pull-up device
according to a modification of the first to third exemplary
embodiments.
[0092] FIG. 10 is a cross-sectional view showing a doping device
according to still another modification of the first to third
exemplary embodiments.
[0093] FIG. 11 is a graph showing a relationship between a
sublimation rate and doping efficiency obtained by an example
according to the first to third exemplary embodiments and a
comparison.
[0094] FIG. 12 is a graph showing a distribution of resistivity of
an ingot obtained by an example according to the first to third
exemplary embodiments and a comparison.
[0095] FIG. 13 is a cross-sectional view showing a pull-up device
according to a fourth exemplary embodiment of the invention.
[0096] FIG. 14 is a cross-sectional view showing a doping device of
the pull-up device.
[0097] FIG. 15 is a schematic view showing a doping process using
the doping device.
[0098] FIG. 16 is a cross-sectional view showing a doping device
according to a modification of the fourth exemplary embodiment of
the invention.
[0099] FIG. 17 is a cross-sectional view showing a pull-up device
according to another modification of the fourth exemplary
embodiment of the invention.
[0100] FIG. 18 is a graph showing comparative results of temporal
dependence of resistivity of an ingot obtained by examples
according to the fourth exemplary embodiment and a comparison.
[0101] FIG. 19 is a cross-sectional view showing a doping device of
a sixth exemplary embodiment of the invention.
[0102] FIG. 20 is a cross-sectional view showing a doping device
according to still another modification of the fifth and sixth
exemplary embodiments.
[0103] FIG. 21 is a graph showing comparative results of temporal
dependence of resistivity of an ingot obtained by an example
according to the fifth and sixth exemplary embodiments and a
comparison.
EXPLANATION OF CODES
[0104] 1 . . . pull-up device; 2, 2', 4, 5, 6, 7, 8 . . . doping
device; 21 . . . outer tube (tube portion); 41, 51, 81 . . . outer
tube; 22, 72 . . . inner tube; 23 . . . heat-shielding member; 30 .
. . chamber; 31 . . . crucible; 34 . . . shield; 64 . . . blow
preventing plate (blow-preventing member); 211 . . . upper portion
(blow-preventing member); 212C . . . through-hole; 213 . . . vane;
221 . . . accommodating portion; 222 . . . cylindrical portion;
231, 231A, 231A1, 231A2, 231B, 231B1, 231B2, 231B3 . . .
heat-shielding plate (heat-shielding member); 412A . . .
through-hole; 422 . . . cylindrical portion (tube); 442B1 . . .
through-hole
BEST MODE FOR CARRYING OUT THE INVENTION
[0105] Embodiment(s) of the present invention will be described
below with reference to the attached drawings.
First Embodiment
[0106] A first exemplary embodiment will be described below with
reference to FIGS. 1 and 2.
[0107] FIG. 1 shows a pull-up device of the exemplary embodiment.
FIG. 2 shows a cross-sectional view showing a doping device of the
pull-up device.
[0108] The pull-up device 1 includes a pull-up device body 3 and a
doping device 2.
[0109] The pull-up device body 3 includes a chamber 30, a crucible
31 disposed inside the chamber 30, a heater 32 for heating the
crucible 31 by heat radiation, a pull-up portion 33, a shield 34
and a heat insulating cylinder 35.
[0110] Inert gas such as argon gas is injected into the chamber 30
from above to below. The inert gas is fed from a pulling-up chamber
surrounded by the pull-up portion 33 on the upper side of the
chamber 30. An entrance of chamber refers to a border area between
the chamber 30 and the pulling-up chamber in the following
description.
[0111] It should be noted that the pressure inside the chamber 30
is adjustable. During the doping process, the flow rate of the
inert gas in the chamber 30 is set at 0.05 m/s or higher and 0.2
m/s or lower, and the pressure of the inert gas is set in a range
from 5332 Pa (converted value of 40 Torr) to 79980 Pa (converted
value of 600 Torr).
[0112] The crucible 31 melts semiconductor wafer material in the
form of polycrystal silicon to prepare a silicon melt. The crucible
31 includes a bottomed cylindrical first crucible 311 made of
quartz and a graphite second crucible 312 disposed outside the
first crucible 311 to accommodate the first crucible 311. The
crucible 31 is supported by a support shaft 36 rotated at a
predetermined speed.
[0113] The heater 32, which is disposed outside the crucible 31,
heats the crucible 31 so as to melt the silicon therein.
[0114] The pull-up portion 33, which is disposed above the crucible
31, is mounted with a seed crystal or the doping device 2. The
pull-up portion 33 is rotatable.
[0115] The heat insulating cylinder 35 is disposed so as to
surround the crucible 31 and the heater 32.
[0116] The shield 34 is a heat-blocking shield for blocking radiant
heat radiated from the heater 32 toward the doping device 2. The
shield 34 surrounds the doping device 2 and covers a surface of the
melt. The shield 34 is configured as a truncated cone having
smaller opening at a lower side than an opening on an upper
side.
[0117] The doping device 2 is a device for volatilizing a solid
dopant and doping the volatilized dopant on the silicon melt in the
crucible 31.
[0118] The dopant may be, for instance, red phosphorus, arsenic and
the like.
[0119] The doping device 2 includes an outer tube 21, an inner tube
22 disposed inside the outer tube 21 and a heat-shielding member
23.
[0120] The outer tube 21, which is cylindrical with its lower end
being opened while its upper end being closed, includes an upper
portion 211 for providing an upper end surface and a lateral
portion 212 that extends downwardly from an outer periphery of the
upper portion 211. In the exemplary embodiment, the lateral portion
212 of the outer tube 21 is configured as a cylinder. The material
of the outer tube 21 is, for instance, transparent quartz.
[0121] A height T of the outer tube 21 is, for instance, 450 mm. A
diameter R of the lateral portion 212 of the outer tube 21 is
preferably 100 mm or more and 1.3 times as large as a pulling-up
crystal diameter or smaller, which is 150 mm for instance.
[0122] The upper portion 211 of the outer tube 21 is provided with
a support 24 that protrudes upwardly from the upper portion 211. By
mounting the support 24 on the pull-up portion 33 of the pull-up
device 1, the outer tube 21 is held by the pull-up device 1.
[0123] The upper portion 211 of the outer tube 21 covers a
later-described accommodating portion 221 of the inner tube 22 from
the above. The upper portion 211 serves as a blow prevention member
for preventing the above-mentioned inert gas that flows from top to
bottom inside the chamber 30 (in other words, from top to bottom of
the accommodating portion 221) from being directly blown against
the accommodating portion 221.
[0124] The inner tube 22 includes an accommodating portion 221 and
a cylindrical portion 222 connected to the accommodating portion
221 to be in communication therewith.
[0125] The material of the inner tube 22 is, for instance,
transparent quartz.
[0126] The accommodating portion 221, which accommodates solid
dopant, is a hollow columnar portion. The accommodating portion 221
includes a substantially plane-circular upper portion 221A, a
bottom portion 221B disposed to face the upper portion 221A, a
lateral portion 221C disposed between outer peripheries of the
upper portion 221A and the bottom portion 221B.
[0127] The center of the bottom portion 221B is provided with an
opening. Solid dopant is placed on the bottom portion 221B around
the opening. When the solid dopant is volatilized, the dopant gas
is ejected through the opening. A circumference of the opening is
provided with a drop preventing wall 221B1 for preventing the solid
dopant from being dropped.
[0128] The position of the dopant housed in the accommodating
portion 221 is, for instance, 300 mm or more above the melt
surface.
[0129] The lateral portion 221C is provided with a support piece(s)
221C1 that is substantially T-shaped in cross section, the support
piece(s) 221C1 protruding outwardly from the accommodating portion
221. By placing the support piece(s) 221C1 on a support(s) 212A
formed on an inner circumference of the outer tube 21, the inner
tube 22 is supported by the outer tube 21.
[0130] The cylindrical portion 222 is a cylindrical member having
open upper and lower end surfaces. An upper end of the cylindrical
portion 222 is connected to the opening on the bottom portion 221B
of the accommodating portion 221.
[0131] A diameter of the cylindrical portion 222 is smaller than
that of the outer tube 21, so that a gap is formed between an outer
circumference of the cylindrical portion 222 and an inner
circumference of the outer tube 21.
[0132] In the present embodiment, the cylindrical portion 222
includes a first cylindrical portion 222A connected to the opening
of the accommodating portion 221 and a second cylindrical portion
222B connected to the first cylindrical portion 222A to extend
downwardly therefrom.
[0133] The first cylindrical portion 222A is integrated with the
accommodating portion 221 while being provided as a body
independent of the second cylindrical portion 222B.
[0134] The first cylindrical portion 222A is provided with a
plurality of ring-shaped grooves 222A1 formed along a
circumferential direction of the first cylindrical portion 222A. In
the present embodiment, three grooves 222A1 are formed. The grooves
222A1 serve to support later-described heat-shielding plates 231 of
the heat-shielding member 23.
[0135] The second cylindrical portion 222B has a diameter of 20 mm
or more and 150 mm or less. Since the second cylindrical portion
222B in the present embodiment is a cylindrical member, its opening
for ejecting the dopant gas also has a diameter in the range from
20 mm to 150 mm. When the outer tube 21 holds the inner tube 22, a
lower distal end of the outer tube 21 protrudes further downward
(toward the melt) than a lower distal end of the second cylindrical
portion 222B.
[0136] The heat-shielding member 23 covers the lower side of the
accommodating portion 221 to block the radiant heat from the melt.
The heat-shielding member 23 has a plurality (exemplarily, five) of
substantially plane-circular heat-shielding plates 231.
[0137] The number of the heat-shielding plates 231 may be
determined in any suitable manner so that the flow volume of the
dopant gas blown onto the melt becomes 3 to 15 litters/min. The
flow volume of the gas flowing out of the lower end of the
cylindrical portion 222 is larger than the flow volume of the
dopant gas evaporating from the melt.
[0138] It is preferable that the number and the position of the
heat-shielding plates 231 are set so that the sublimation rate of
the dopant accommodated in the accommodating portion 221 becomes 10
to 50 g/min.
[0139] The outer diameter of the heat-shielding plates 231 is
substantially equal to the inner diameter of the outer tube 21. The
centers of the heat-shielding plates 231 are provided with holes
2311 into which the cylindrical portion 222 is inserted. The
heat-shielding plates 231 are substantially horizontally disposed
to shield the gap between the cylindrical portion 222 of the inner
tube 22 and the outer tube 21 and to be substantially parallel to
one another.
[0140] In the exemplary embodiment, two heat-shielding plates 231A
of the five heat-shielding plates 231 near the melt are provided by
graphite members, whereas three heat-shielding plates 231B on the
side of the accommodating portion 221 are provided by quartz
members.
[0141] The plurality of heat-shielding plates 231 are disposed in
the order of the two heat-shielding plates 231A and the three
heat-shielding plates 231B from the lower end of the cylindrical
portion 222.
[0142] The heat-shielding plates 231A are supported by the outer
tube 21 such that projections 212B formed on inner sides of the
outer tube 21 support the outer peripheries of the heat-shielding
plates 231A. A heat-shielding plate 231A (231A1) that is the
closest to the melt is disposed, for example, approximately 80 mm
above the lower distal end of the cylindrical portion 222.
[0143] A heat-shielding plate 231A2 above the heat-shielding plate
231A1 is disposed, for example, approximately 170 mm above the
lower distal end of the cylindrical portion 222. Hence, a gap of
approximately 90 mm is formed between the heat-shielding plate
231A1 and the heat-shielding plate 231A2.
[0144] On the other hand, the heat-shielding plates 231B are
supported by the inner tube 22 such that the peripheries of the
holes 2311 are supported by the grooves 222A1 of the first
cylindrical portion 222A of the cylindrical portion 222 of the
inner tube 22.
[0145] Among the three heat-shielding plates 231B, a heat-shielding
plate 231B1 that is the closest to the melt is disposed, for
example, approximately 250 mm above the lower distal end of the
cylindrical portion 222.
[0146] A heat-shielding plate 231B2 above the heat-shielding plate
231B1 is disposed, for example, approximately 10 mm above the
heat-shielding plate 231B1.
[0147] A heat-shielding plate 231B3 further above the
heat-shielding plate 231B1 is disposed, for example, approximately
10 mm above the heat-shielding plate 231B2. In other words, gaps of
a predetermined size are formed between the heat-shielding plates
231B.
[0148] The distance between the heat-shielding plate 231B1 and the
accommodating portion 221 is exemplarily 30 mm.
[0149] Thus arranged doping device 2 is assembled as follows.
[0150] Initially, solid dopant is inserted into the accommodating
portion 221 of the inner tube 22.
[0151] Next, the heat-shielding plate 231B is attached to the first
cylindrical portion 222A of the cylindrical portion 222 integrated
with the accommodating portion 221. Specifically, the first
cylindrical portion 222A is inserted to the central hole 2311 of
the respective heat-shielding plates 231B and the peripheries of
the holes 2311 of the heat-shielding plates 231B are engaged with
the respective grooves 222A1 of the first cylindrical portion
222A.
[0152] Subsequently, the first cylindrical portion 222A and the
heat-shielding plates 231B are inserted into the outer tube 21 and
the support piece 221C of the accommodating portion 221 is placed
on the support 212A provided on the outer tube 21.
[0153] Next, the heat-shielding plates 231A are inserted into the
outer tube 21 and the outer circumference of the heat-shielding
plates 231A is supported by the projections 212B of the outer tube
21.
[0154] Finally, the second cylindrical portion 222B of the
cylindrical portion 222 of the inner tube 22 is inserted into the
outer tube 21. Specifically, the second cylindrical portion 222B is
inserted into the holes 2311 provided at the center of the
heat-shielding plates 231A supported by the outer tube 21. Then,
the upper end of the second cylindrical portion 222B and the lower
end of the first cylindrical portion 222A are connected.
[0155] The doping device 2 is assembled as described above.
[0156] When using the assembled doping device 2, the support 24
provided on the outer tube 21 of the doping device 2 is attached to
the pull-up portion 33 of the pull-up device 1.
[0157] Inert gas is subsequently flowed from above the pull-up
device 1 toward the melt. The inert gas flows along the surface of
the melt.
[0158] The inert gas is continuously flowed during conducting the
doping and pulling up a grown crystal. The flow volume of the inert
gas is in a range from 50 litters/min to 400 litters/min. The flow
rate of the inert gas at the entrance of the chamber 30 is in a
range from 0.05 m/s to 0.2 m/s. When the flow volume of the inert
gas is set to exceed 400 litters/min, the accommodating portion 221
may be so cooled that the dopant is not volatilized or the
sublimated dopant may be solidified and adhered.
[0159] Next, the lower end of the outer tube 21 is immersed in the
melt. At this time, the lower end of the cylindrical portion 222 of
the inner tube 22 is set so as not to touch the melt.
[0160] The dopant placed inside the accommodating portion 221 of
the doping device 2 is gradually sublimated by the heat from the
melt, such that the dopant in a gas form is ejected from the
cylindrical portion 222 of the doping device 2 to be dissolved in
the melt.
[0161] A temperature of the melt in the crucible 31 at the time of
doping is in a range from a melting point of a material of the melt
to 60.degree. C. above the melting point. In the present
embodiment, since the material of the melt is silicon, the
temperature of the melt is set to be in a range from 1412.degree.
C. to 1472.degree. C.
[0162] When the gas is dissolved in the melt, the pull-up portion
33 of the pull-up device 1 is detached from the doping device 2 and
mounted with the seed crystal. Then, the pulling-up of the grown
crystal is started.
[0163] According to the present embodiment, the following effects
can be obtained.
[0164] (1-1) The shield 34 is provided on the pull-up device 1 so
that the shield 34 surrounds the doping device 2 to cover the melt
surface. In addition, the doping device 2 includes the
heat-shielding plate 231 that shields transmission of heat ray from
the melt. The heat-shielding plate 231 is disposed to cover a lower
side of the accommodating portion 221 that accommodates the
dopant.
[0165] Accordingly, the shield 34 and the heat-shielding plate 231
reliably prevent the transfer of the radiant heat of the melt to
the accommodating portion 221, so that the sublimation rate of the
dopant within the accommodating portion 221 becomes 10 g/min or
higher and 50 g/min or lower, which is slower than the sublimation
rate in a traditional doping device.
[0166] Thus, the dopant is not instantaneously volatilized and the
blowing pressure of the dopant gas to the melt can be lowered.
[0167] Further, since it can be prevented that time allowance for
dissolving the dopant into the melt is lost on account of
excessively ejected dopant gas, the dopant can be sufficiently
dissolved into the melt, so that absorption rate is not
deteriorated. Further, it can be prevented that the formation of
monocrystal is hindered by the blown-off silicon to make it
difficult to manufacture semiconductor wafers having a desired
resistance value.
[0168] (1-2) In this exemplary embodiment, the temperature of the
melt when being doped is set at the melting point of silicon or
higher and 60.degree. C. above the melting point or lower.
[0169] When the temperature of the melt is lower than the melting
point of silicon, in the event that the melt temperature is low
during the doping process, the surface of the melt may be
solidified as a result of lowered silicon temperature when the
doping tube is immersed or the gas is blown, so that the gas is not
easily absorbed.
[0170] On the other hand, when the melt temperature exceeds the
point 60.degree. C. above the melting point, the melt may be
boiled. Further, when the melt temperature exceeds the point
60.degree. C. above the melting point, evaporation of the dopant
gas absorbed in the melt may be promoted to lower the dopant
absorption efficiency.
[0171] Since the temperature of the melt is set at the melting
point of silicon or higher and 60.degree. C. above the melting
point or lower in this exemplary embodiment, the above problems can
be avoided.
[0172] (1-3) When the pressure inside the chamber 30 is less than
5332 Pa (converted value of 40 Torr) during the doping process, the
dopant dissolved in the melt may be easily volatilized.
[0173] On the other hand, when the pressure inside the chamber 30
exceeds 79980 Pa (converted value of 600 Torr), though
volatilization of the dopant from the melt can be restrained, high
pressure resistance and heat resistance are required for the
chamber 30, which incurs additional production cost.
[0174] In the exemplary embodiment, since the pressure inside the
chamber 30 when being doped is set within the above range, the
above problem can be avoided.
[0175] (1-4) The flow volume of the inert gas flowing from above to
below the accommodating portion 221 of the doping device 2 is set
in a range from 50 litters/min to 400 litters/min and the flow rate
at the entrance of the chamber 30 is set in a range from 0.05 m/s
to 0.2 m/s. Accordingly, the accommodating portion 221 can be
cooled by the inert gas, thus allowing adjustment of the
sublimation rate of the dopant in the accommodating portion
221.
[0176] (1-5) Since the diameter of the ejecting opening of the gas
on the second cylindrical portion 222B of the inner tube 22 is 20
mm or more, the volatilized dopant gas is not vigorously blown onto
the melt, so that blow-off of the melt can be reliably avoided.
[0177] (1-6) If the position of the dopant is located very close to
the surface of the melt when being doped, the dopant is disposed in
a high temperature atmosphere due to the heat of the melt, so that
it may become difficult to control the sublimation rate of the
dopant.
[0178] In this exemplary embodiment, since the position of the
dopant is located 300 mm or more above the surface of the melt, the
sublimation rate of the dopant can be reliably controlled.
[0179] (1-7) The doping device 2 is provided with the cylindrical
portion 222 having an upper end in communication with the
accommodating portion 221 to guide the volatilized dopant gas to
the melt. Since the cylindrical portion 222 is provided, the
volatilized dopant gas can be reliably guided to the melt, so that
the doping efficiency to the melt can be enhanced.
[0180] (1-8) Further, the doping device 2 of the exemplary
embodiment includes the cylindrical outer tube 21 that has an
opening on the lower end surface and accommodates the inner tube 22
having the accommodating portion 221 and the cylindrical portion
222. When the inert gas is flowed from the upper side of the melt
to the surface of the melt in doping the melt, since the doping
device 2 includes the outer tube 21 that houses the inner tube 22,
the inert gas is not directly blown to the inner tube 22.
Accordingly, it can be avoided that the inner tube 22 is cooled by
the inert gas to be lower than the evaporation temperature of the
dopant.
[0181] (1-9) In this exemplary embodiment, the lower end of the
outer tube 21 of the doping device 2 is projected toward the melt
relative to the lower end of the cylindrical portion 222 of the
inner tube 22 so that only the lower end of the outer tube 21 is
immersed in the melt to dope the melt.
[0182] Accordingly, even when a part of the gas ejected from the
cylindrical portion 222 of the inner tube 22 is not dissolved into
the melt, the gas resides within a space defined by the cylindrical
portion 222 of the inner tube 22, the outer tube 21 and the
heat-shielding plate 231 without being ejected outside the doping
device 2, so that the doping efficiency can be enhanced.
[0183] (1-10) When the melt is doped, only the lower end of the
outer tube 21 is immersed in the melt without immersing the lower
end of the cylindrical portion 222 of the inner tube 22, the heat
of the melt is not directly transferred to the inner tube 22.
Accordingly, the temperature of the accommodating portion 221 is
not raised on account of the heat of the melt directly transferred
to the inner tube 22. Thus, the sublimation rate of the dopant in
the accommodating portion 221 is not increased.
[0184] (1-11) In this exemplary embodiment, the plurality of
heat-shielding plates 231 disposed between the outer tube 21 and
the inner tube 22 and covering the lower side of the accommodating
portion 221 of the inner tube 22 are provided. Accordingly, the
heat ray from the melt can be reliably shielded and the sublimation
rate of the dopant in the accommodating portion 221 can be
lowered.
[0185] (1-12) Since the heat conductivity of the heat-shielding
plate 231 (231B) closest to the accommodating portion 221 of the
inner tube 22 of the doping device 2 is relatively high, the heat
is not accumulated in the heat-shielding plate 231B closest to the
accommodating portion 221. Accordingly, since the accommodating
portion 221 is not heated by the heat accumulated in the
heat-shielding plate 231B, the sublimation rate of the dopant in
the accommodating portion 221 is not accelerated by the presence of
the heat-shielding plate 231B.
[0186] Further, since the heat conductivity of the heat-shielding
plate 231A closest to the melt is relatively low, the heat
transmission from the melt can be blocked at a position remote from
the accommodating portion 221, which also contributes to prevention
of increase in the sublimation rate of the dopant in the
accommodating portion 221.
[0187] (1-13) Since the plurality of heat-shielding plates 231 are
spaced apart by a predetermined gap, the heat is not easily
accumulated in the respective heat-shielding plates 231 as compared
with an arrangement in which the heat-shielding plates are
superposed.
Second Embodiment
[0188] Next, a second exemplary embodiment of the invention will be
described below. In the following description, the same components
as those having been explained above will be referenced with the
same numeral to omit the description thereof.
[0189] As shown in FIGS. 3 and 4, the doping device 4 of this
exemplary embodiment includes the same inner tube 22 as that of the
first exemplary embodiment and an outer tube 41 that surrounds the
inner tube 22. In other words, the only difference between the
doping device 4 of this exemplary embodiment and the doping device
2 of the first exemplary embodiment is the structure of the outer
tube.
[0190] The outer tube 41, which is bottomed-cylindrical with its
lower end being opened while its upper end being closed, includes
an upper portion 211 and a lateral portion 412 that extends
downwardly from an outer periphery of the upper portion 211. In the
exemplary embodiment, the lateral portion 412 of the outer tube 41
is configured as a cylinder. The material of the outer tube 41 is,
for instance, transparent quartz as in the first exemplary
embodiment. The height and diameter of the outer tube 41 are the
same as the outer tube 21 of the first exemplary embodiment.
[0191] The lateral portion 412 protrudes toward the melt relative
to the lower end of the cylindrical portion 222 of the inner tube
22 so that the lower end of the lateral portion 412 is immersed in
the melt.
[0192] A plurality of through-holes 412A are provided on the lower
end (the portion immersed in the melt) of the lateral portion 412
at a regular interval along the circumference thereof.
[0193] Further, a plurality of vanes 413 are provided on the outer
circumference of the lateral portion 412 adjacent to the
through-holes 412A.
[0194] The vanes 413 are arranged so that vane surfaces thereof are
aligned with the axis of the outer tube 41 of the doping device 4.
Further, though described later in detail, the doping device 4 is
rotated around the central axis of the outer tube 41 when the melt
is doped, where the vanes 413 are provided rearward relative to the
rotary direction of the outer tube 41 (see FIG. 5).
[0195] In this exemplary embodiment, the doping device 4 is used to
dope the melt as follows. Incidentally, the pressure in the chamber
30, the flow volume and flow rate of the inert gas, the temperature
of the melt, the position of the dopant from the melt surface and
the sublimation rate of the dopant gas blown onto the melt when the
doping process is conducted are the same as those in the first
exemplary embodiment.
[0196] Initially, while rotating the crucible 31 in advance, the
lower end of the outer tube 41 is immersed in the melt. At this
time, the lower end of the cylindrical portion 222 of the inner
tube 22 is set so as not to touch the melt.
[0197] Further, as shown in FIG. 5, the doping device 4 is rotated
around the central axis of the outer tube 41 in a direction
opposite to the rotary direction of the crucible 31. In FIG. 5, an
arrow Y1 indicates the rotary direction of the crucible 31, whereas
an arrow Y2 indicates the rotary direction of the doping device
4.
[0198] The dopant placed inside the accommodating portion 221 of
the doping device 4 is gradually sublimated by the heat from the
melt, such that the dopant in a gas form is ejected from the
cylindrical portion 222 of the doping device 2.
[0199] By rotating the doping device 4 and the crucible 31, the
melt outside the outer tube 41 collides with the vane 413 provided
on the outer tube 41 to be introduced to the interior of the outer
tube 41 through the through-hole 412A as shown in an arrow Y3 in
FIG. 5. The melt inside the outer tube 41 is gradually ejected from
the lower side of the outer tube 41 to form a flow in a direction
of an arrow Y4 shown in FIG. 3. In other words, the melt surface on
which the gas ejected from the cylindrical portion 222 of the inner
tube 22 is stirred, so that the gas is always blown on a new melt
surface. Further, the melt in which the gas is dissolved is ejected
from the opening on the lower end of the outer tube 41.
[0200] According to this exemplary embodiment, as well as the
effects (1-1) to (1-13) of the first exemplary embodiment,
following effects can be obtained.
[0201] (2-1) The doping device 4 is provided with the outer tube 41
having the through-hole 412A at the portion immersed in the melt.
Further, the doping device 4 and the crucible 31 are reversely
rotated with each other when the melt is doped. By rotating the
doping device 4 and the crucible 31, the melt outside the outer
tube 41 collides with the vane 413 provided on the outer tube 41 to
be introduced to the interior of the outer tube 41 through the
through-hole 412A to be subjected to the blow of the dopant gas.
Then, the melt having been subjected to the blow of the gas is
gradually discharged from the opening on the lower end of the outer
tube 41.
[0202] Since the new melt is always introduced to the portion
within the outer tube 41 at which the gas is blown from the inner
tube 22, the absorption efficiency of the dopant gas can be
enhanced.
[0203] (2-2) Further, since the melt in which the dopant gas is
dissolved is discharged from the opening on the lower end of the
outer tube 41, the gas containing the dopant no more exists on the
surface of the melt, so that the evaporation of the dopant from the
melt can be restrained, thus further enhancing the doping
efficiency.
Third Embodiment
[0204] Next, a third exemplary embodiment will be described below
with reference to FIG. 6.
[0205] A doping device 5 of this exemplary embodiment has the same
inner tube 22, support 24 and heat-shielding member 23 as the first
exemplary embodiment, an outer tube 51 and a tube 55 disposed
between the outer tube 51 and the inner tube 22.
[0206] The outer tube 51 has approximately the same structure as
the outer tube 21 of the first exemplary embodiment except that a
plurality of projections 512A extending toward the inside of the
outer tube 51 are provided on an inside of the lower end of the
outer tube 51. The other arrangement of the outer tube 51 is the
same as the outer tube 21 of the first exemplary embodiment.
[0207] The tube 55 has open upper and lower end surfaces and has a
diameter smaller than the outer tube 51 and greater than the
cylindrical portion 222 of the inner tube 22. The tube 55 is
disposed on the projections 512A and is located between the outer
tube 51 and the inner tube 22.A gap is provided between the inner
circumference of the lateral portion 212 of the outer tube 51 and
the outer circumference of the tube 55. A gap is also provided
between the inner circumference of the tube 55 and the cylindrical
portion 222 of the inner tube 22.
[0208] The height of the tube 55 is smaller than a distance from
the lower end of the outer tube 51 to the heat-shielding plate 231A
(231A1) closest to the melt, so that a gap is provided between the
tube 55 and the heat-shielding plate 231A (231A1).
[0209] In this exemplary embodiment, the doping device 5 is used to
dope the melt as follows. Incidentally, the pressure in the chamber
30, the flow volume and flow rate of the inert gas, the temperature
of the melt, the position of the dopant from the melt surface and
the sublimation rate of the dopant gas blown onto the melt when the
doping process is conducted are the same as those in the above
embodiments.
[0210] While rotating the crucible 31 in advance, the lower end of
the outer tube 51 is immersed in the melt. At this time, the lower
end of the cylindrical portion 222 of the inner tube 22 and the
lower end of the tube 55 are set so as not to touch the melt.
[0211] The dopant placed inside the accommodating portion 221 of
the doping device 5 is gradually sublimated by the heat from the
melt, such that the dopant in a gas form is ejected from the
cylindrical portion 222 of the doping device 5 to be dissolved in
the melt.
[0212] At this time, a part of the gas ejected from the cylindrical
portion 222 escapes to the outside of the cylindrical portion 222
without being dissolved in the melt. Further, a part of the gas is
reflected on the surface of the melt without being dissolved in the
melt. The part of gas passes through the gap between the outer
circumference of the lower end of the cylindrical portion 222 and
the inner circumference of the tube 55 to go up, and subsequently
is reflected by the heat-shielding plate 231 to be introduced
between the cylindrical portion 222 and the outer circumference of
the lateral portion 212 of the tube 55. Then, the gas is introduced
to the melt surface (see arrow Y5 in FIG. 6).
[0213] In other words, the gap between the outer circumference of
the lower end of the cylindrical portion 222 and the inner
circumference of the tube 55 and the gap between the inner
circumference of the outer tube 51 and the outer circumference of
the tube 55 define a path for introducing the gas to the melt
surface.
[0214] According to this exemplary embodiment, as well as the
effects (1-1) to (1-13) of the first exemplary embodiment,
following effects can be obtained.
[0215] (3-1) The doping device 5 includes the tube 55 disposed
between the outer tube 51 and the inner tube 22. A part of the gas
ejected from the cylindrical portion 222 and not dissolved in the
melt passes through the gap between the outer circumference of the
lower end of the cylindrical portion 222 and the inner
circumference of the tube 55, goes up and subsequently is reflected
by the heat-shielding plate 231 to be introduced to the space
between the inner circumference of the outer tube 51 and the outer
circumference of the tube 55. Then, the gas is re-introduced to the
melt surface. Since the gas not dissolved in the melt can be
introduced to the melt surface again, the doping efficiency can be
enhanced.
Modification(s) of First to Third Embodiments
[0216] The present invention is not limited to the above-described
embodiments but may include modifications and improvements made
within a scope where an object of the present invention can be
achieved.
[0217] For instance, though the doping devices 2, 4, 5 of the
exemplary embodiments include the outer tubes 21, 41, 51, the outer
tube may not be provided. For instance, as shown in FIG. 7, a
blow-preventing plate 64 for preventing a blow of the gas to the
accommodating portion 221 of the inner tube 22 may be provided
above the accommodating portion 221 in place of the outer tube.
When the doping device 6 having no outer tube is used, all of the
heat-shielding plates 231 are preferably fixed on the inner tube
22.
[0218] As shown in FIG. 8, when the melt is to be stirred in a
doping device 7 having no outer tube, through-holes 222B1 may be
provided on the inner tube 72 and vanes 413 may be provided
adjacent to the through-holes 222B1. The inner tube 72 is the same
as the inner tube 22 of the first exemplary embodiment except for
the provision of the through-holes 222B1 and the vanes 413.
[0219] Though the lower end of the outer tubes 21, 41, 51 of the
doping devices 2, 4, 5 protrude relative to the lower end of the
inner tube 22 in the respective exemplary embodiments, the lower
end of the inner tube 22 and the lower end of the outer tube may be
situated at the same level relative to the melt.
[0220] Though the doping devices 2, 4, 5 of the respective
exemplary embodiments include the heat-shielding plates 231
covering the lower side of the accommodating portion 221 of the
inner tube 22, the doping device may alternatively be provided with
a heat-shielding member covering the lateral portion 221C as well
as the lower side of the accommodating portion 221. For instance, a
heat-insulating material may be wound on the lateral portion 221C
and the bottom portion 221B of the accommodating portion 221. With
this arrangement, the transmission of the radiant heat from the
melt to the accommodating portion 221 can be further reliably
prevented.
[0221] The doping device 4 is rotated to form the flow in the arrow
Y4 shown in FIG. 3 to enhance the doping efficiency when the melt
is doped in the second exemplary embodiment. However, as shown in
FIG. 9 for instance, a doping device 8 having an outer tube 81
provided with a through-hole 812A on the lower end of a lateral
portion 812 may be vertically driven (in a direction of an arrow
Y5) to stir the melt. The doping device 8 is the same as the doping
device 2 of the first exemplary embodiment except that the outer
tube 81 is provided with the lateral portion 812 having the
through-hole 812A.
[0222] By vertically driving the doping device 8, the melt can be
stirred and the temperature of the accommodating portion 221 of the
inner tube 22 can be adjusted to control the sublimation rate of
the dopant.
[0223] The radiation of radiant heat of the melt to the
accommodating portion 221 is blocked by the heat-shielding member
23 and the shield 34 in the above respective exemplary embodiments.
However, for instance, a heat-shielding plate 25 may be provided on
the lateral portion 212 of the outer tube 21 of a doping device 2'
as shown in FIG. 10 and the radiation of the radiant heat of the
melt to the accommodating portion 221 may be blocked by the
heat-shielding plate 25, the heat-shielding member 23 and the
shield 34. Incidentally, the doping device 2' shown in FIG. 10 is
the same as the doping device 2 in the first exemplary embodiment
except for the provision of the heat-shielding plate 25.
[0224] Though the doping device 4 is rotated to stir the melt to
enhance the doping efficiency in the second exemplary embodiment,
the tube 55 of the third exemplary embodiment may be provided on
the doping device 4 of the second exemplary embodiment.
Accordingly, since the path for re-introducing the gas not
dissolved in the melt is formed, the doping efficiency can be
further enhanced.
[0225] Though the doping conditions of the respective exemplary
embodiments are defined as: the temperature of the melt at the
melting point of silicon or higher and 60.degree. C. above the
melting point or lower; the flow volume of the inert gas flowing
from above to below the accommodating portion 221 of the doping
device being in a range from 50 litters/min to 400 litters/min; and
the pressure inside the chamber 30 being 5332 Pa or more and 79980
Pa or less, the doping process may be conducted out of the above
range.
Fourth Embodiment
[0226] Next, a fourth exemplary embodiment of the invention will be
described below.
[0227] FIG. 13 shows a pull-up device of this exemplary embodiment.
FIG. 14 shows a cross-sectional view showing a doping device of the
pull-up device.
[0228] The pull-up device 1 includes a pull-up device body 3 and a
doping device 2.
[0229] The pull-up device body 3 includes a chamber 30, a crucible
31 disposed inside the chamber 30, a heater 32 for heating the
crucible 31 by heat radiation, a pull-up portion 33, a shield 34
and a heat insulating cylinder 35.
[0230] Inert gas such as argon gas is injected into the chamber 30
from above to below. The pressure inside the chamber 30 is
adjustable. During the doping process, the pressure of the inert
gas is set in a range from 5332 Pa (converted value of 40 Torr) to
79980 Pa (converted value of 600 Torr).
[0231] The crucible 31 melts semiconductor material in the form of
polycrystal silicon to prepare a melt. The crucible 31 includes a
bottomed cylindrical first crucible 311 made of quartz and a
graphite second crucible 312 disposed outside the first crucible
311 to accommodate the first crucible 311. The crucible 31 is
supported by a support shaft 36 rotated at a predetermined
speed.
[0232] The heater 32, which is disposed outside the crucible 31,
heats the crucible 31 so as to melt the silicon therein.
[0233] The pull-up portion 33, which is disposed above the crucible
31, is mounted with a seed crystal or the doping device 2. The
pull-up portion 33 is rotatable.
[0234] The heat insulating cylinder 35 is disposed so as to
surround the crucible 31 and the heater 32.
[0235] The shield 34 is a heat-blocking shield for blocking radiant
heat radiated from the heater 32 toward the doping device 2. The
shield 34 surrounds the doping device 2 and covers a surface of the
melt. The shield 34 is configured as a truncated cone having
smaller opening at a lower side than an opening on an upper
side.
[0236] The doping device 2 is a device for volatilizing a solid
dopant and doping the volatilized dopant on the silicon melt in the
crucible 31.
[0237] The dopant may be, for instance, red phosphorus, arsenic and
the like.
[0238] The doping device 2 includes an outer tube (tube portion)
21, an inner tube 22 disposed inside the outer tube 21 and a
heat-shielding member 23.
[0239] The outer tube 21 accommodates the inner tube 22, in which
the dopant gas from the inner tube 22 is introduced. In other
words, the outer tube 21 works as the tube portion of the
invention.
[0240] The outer tube 21, which is bottomed-cylindrical with its
lower end being opened while its upper end being closed, includes
an upper portion 211 for providing an upper end surface and a
lateral portion 212 that extends downwardly from an outer periphery
of the upper portion 211. In the exemplary embodiment, the lateral
portion 212 of the outer tube 21 is configured as a cylinder. The
material of the outer tube 21 is, for instance, transparent
quartz.
[0241] A height T of the outer tube 21 is, for instance, 450 mm. A
diameter R of the lateral portion 212 of the outer tube 21 is
preferably 100 mm or more and 1.3 times as large as a pull-up
diameter or smaller.
[0242] The upper portion 211 of the outer tube 21 is provided with
a support 24 that protrudes upwardly from the upper portion 211.By
mounting the support 24 on the pull-up portion 33 of the pull-up
device 1, the outer tube 21 is held by the pull-up device 1.
[0243] The upper portion 211 of the outer tube 21 covers a
later-described accommodating portion 221 of the inner tube 22 from
the above. The upper portion 211 serves as a blow prevention member
for preventing the above-mentioned inert gas that flows from top to
bottom inside the chamber 30 (in other words, from top to bottom of
the accommodating portion 221) from being directly blown against
the accommodating portion 221.
[0244] A plurality of through-holes 212C are provided on the lower
end (the portion immersed in the melt) of the lateral portion 212
of the outer tube 21 at a regular interval along the circumference
thereof.
[0245] Further, a plurality of vanes 213 are provided on the outer
circumference of the lateral portion 212 adjacent to the
through-holes 212C.
[0246] The vanes 213 are arranged so that vane surfaces thereof are
aligned with the axis of the outer tube 21 of the doping device 2.
Further, the doping device 2 is rotated around the central axis of
the outer tube 21 when the melt is doped, where the vanes 213 are
provided on a rear end of the outer tube 21 in the rotary direction
(see FIG. 15).
[0247] The inner tube 22 includes an accommodating portion 221 and
a cylindrical portion 222 connected to the accommodating portion
221 to be in communication therewith.
[0248] The material of the inner tube 22 is, for instance,
transparent quartz.
[0249] The accommodating portion 221, which accommodates solid
dopant, is a hollow columnar portion. The accommodating portion 221
includes a substantially plane-circular upper portion 221A, a
bottom portion 221B disposed to face the upper portion 221A, a
lateral portion 221C disposed between outer peripheries of the
upper portion 221A and the bottom portion 221B.
[0250] The center of the bottom portion 221B is provided with an
opening. Solid dopant is placed on the bottom portion 221B around
the opening. When the solid dopant is volatilized, the dopant gas
is ejected through the opening. A circumference of the opening is
provided with a drop preventing wall 221B1 for preventing the solid
dopant from being dropped.
[0251] The dopant accommodated in the accommodating portion 221 is
preferably positioned at a position where its temperature
approaches the sublimation temperature of the dopant because, when
the accommodating portion 221 is close to the melt surface, high
temperature therefrom deteriorates thermal insulating effects. In
this embodiment, the dopant is exemplarily placed approximately 300
mm away from the surface of the melt.
[0252] The lateral portion 221C is provided with a support piece(s)
221C1 that is substantially T-shaped in cross section, the support
piece(s) 221C1 protruding outwardly from the accommodating portion
221. By placing the support piece(s) 221C1 on a support(s) 212A
formed on an inner circumference of the outer tube 21, the inner
tube 22 is supported by the outer tube 21.
[0253] The cylindrical portion 222 is a cylindrical member having
open upper and lower end surfaces. An upper end of the cylindrical
portion 222 is connected to the opening on the bottom portion 221B
of the accommodating portion 221.
[0254] A diameter of the cylindrical portion 222 is smaller than
that of the outer tube 21, so that a gap is formed between an outer
circumference of the cylindrical portion 222 and an inner
circumference of the outer tube 21.
[0255] In the present embodiment, the cylindrical portion 222
includes a first cylindrical portion 222A connected to the opening
of the accommodating portion 221 and a second cylindrical portion
222B connected to the first cylindrical portion 222A to extend
downwardly therefrom.
[0256] The first cylindrical portion 222A is integrated with the
accommodating portion 221 while being provided as a body
independent of the second cylindrical portion 222B.
[0257] The first cylindrical portion 222A is provided with a
plurality of ring-shaped grooves 222A1 formed along a
circumferential direction of the first cylindrical portion 222A. In
the present embodiment, three grooves 222A1 are formed. The grooves
222A1 serve to support later-described heat-shielding plates 231 of
the heat-shielding member 23.
[0258] The second cylindrical portion 222B has a diameter of 20 mm
or more and 150 mm or less. Since the second cylindrical portion
222B in the present embodiment is a cylindrical member, its opening
for ejecting the dopant gas also has a diameter in the range from
20 mm to 150 mm. When the outer tube 21 holds the inner tube 22, a
lower distal end of the outer tube 21 protrudes further downward
(toward the melt) than a lower distal end of the second cylindrical
portion 222B.
[0259] The heat-shielding member 23 covers the lower side of the
accommodating portion 221 to block the radiant heat from the melt.
The heat-shielding member 23 has a plurality (exemplarily, five) of
substantially plane-circular heat-shielding plates 231.
[0260] The number of the heat-shielding plates 231 may be
determined in any suitable manner so that the flow rate of the
dopant gas blown onto the melt becomes 3 to 15 L/min. The flow rate
of the gas flowing out of the lower end of the cylindrical portion
222 is larger than the flow rate of the evaporant evaporating from
the melt.
[0261] The sublimation rate of the dopant housed in the
accommodating portion 221 is 10 to 50 g/min.
[0262] The outer diameter of the heat-shielding plates 231 is
substantially equal to the inner diameter of the outer tube 21. The
centers of the heat-shielding plates 231 are provided with holes
2311 into which the cylindrical portion 222 is inserted. The
heat-shielding plates 231 are substantially horizontally disposed
to shield the gap between the cylindrical portion 222 of the inner
tube 22 and the outer tube 21 and to be substantially parallel to
one another.
[0263] In the present embodiment, among the five heat-shielding
plates 231, heat-shielding plates 231A disposed adjacently to the
melt may be made of, for example, carbon heat-insulating material.
The carbon heat-insulating material is formed by impregnating a
material such as a thermoplastic resin with carbon fibers, curing
the material by heating and burning the material under vacuum or
under an atmosphere of inert gas. For heat conductivity of the
heat-shielding plates 231A, a material whose heat conductivity is
20 W/m.degree. C. at 1412.degree. C. may be exemplarily used.
[0264] Among the five heat-shielding plates 231, three
heat-shielding plates 231B disposed adjacently to the accommodating
portion 221 maybe made of opaque quartz. Opaque quartz is formed
by, for example, impregnating quartz glass with multiple fine
bubbles. For heat conductivity of the heat-shielding plates 231B, a
material whose heat conductivity is 8 W/m.degree. C. at
1412.degree. C. maybe exemplarily used.
[0265] The plurality of heat-shielding plates 231 are disposed in
the order of the two heat-shielding plates 231A and the three
heat-shielding plates 231B from the lower end of the cylindrical
portion 222.
[0266] The heat-shielding plates 231A are supported by the outer
tube 21 such that projections 212B formed on inner sides of the
outer tube 21 support the outer peripheries of the heat-shielding
plates 231A. A heat-shielding plate 231A (231A1) that is the
closest to the melt is disposed, for example, approximately 80 mm
above the lower distal end of the cylindrical portion 222.
[0267] A heat-shielding plate 231A2 above the heat-shielding plate
231A1 is disposed, for example, approximately 170 mm above the
lower distal end of the cylindrical portion 222. Hence, a gap of
approximately 90 mm is formed between the heat-shielding plate
231A1 and the heat-shielding plate 231A2.
[0268] On the other hand, the heat-shielding plates 231B are
supported by the inner tube 22 such that the peripheries of the
holes 2311 are supported by the grooves 222A1 of the first
cylindrical portion 222A of the cylindrical portion 222 of the
inner tube 22.
[0269] Among the three heat-shielding plates 231B, a heat-shielding
plate 231B1 that is the closest to the melt is disposed, for
example, approximately 250 mm above the lower distal end of the
cylindrical portion 222.
[0270] A heat-shielding plate 231B2 above the heat-shielding plate
231B1 is disposed, for example, approximately 10 mm above the
heat-shielding plate 231B1.
[0271] A heat-shielding plate 231B3 further above the
heat-shielding plate 231B1 is disposed, for example, approximately
10 mm above the heat-shielding plate 231B2. In other words, gaps of
a predetermined size are formed between the heat-shielding plates
231B.
[0272] The distance between the heat-shielding plate 231B1 and the
accommodating portion 221 is exemplarily 30 mm.
[0273] Thus arranged doping device 2 is assembled as follows.
[0274] Initially, solid dopant is inserted into the accommodating
portion 221 of the inner tube 22.
[0275] Next, the heat-shielding plate 231B is attached to the first
cylindrical portion 222A of the cylindrical portion 222 integrated
with the accommodating portion 221. Specifically, the first
cylindrical portion 222A is inserted to the central hole 2311 of
the respective heat-shielding plates 231A and the peripheries of
the holes 2311 of the heat-shielding plates 231B are engaged with
the respective grooves 222A1 of the first cylindrical portion
222A.
[0276] Subsequently, the first cylindrical portion 222A and the
heat-shielding plates 231B are inserted into the outer tube 21 and
the support piece 221C of the accommodating portion 221 is placed
on the support 212A provided on the outer tube 21.
[0277] Next, the heat-shielding plates 231A are inserted into the
outer tube 21 and the outer circumference of the heat-shielding
plates 231A is supported by the projections 212B of the outer tube
21.
[0278] Finally, the second cylindrical portion 222B of the
cylindrical portion 222 of the inner tube 22 is inserted into the
outer tube 21. Specifically, the second cylindrical portion 222B is
inserted into the holes 2311 provided at the center of the
heat-shielding plates 231A supported by the outer tube 21. Then,
the upper end of the second cylindrical portion 222B and the lower
end of the first cylindrical portion 222A are connected.
[0279] The doping device 2 is assembled as described above.
[0280] When using the assembled doping device 2, the support 24
provided on the outer tube 21 of the doping device 2 is attached to
the pull-up portion 33 of the pull-up device 1.
[0281] Inert gas is subsequently flowed from an upper side of the
pull-up device 1 toward the melt. The inert gas flows along the
surface of the melt.
[0282] The inert gas is continuously flowed during conducting the
doping and pulling up a grown crystal. The flow rate of the inert
gas is set to be in a range of in a range from 50 litters/min to
400 litters/min. When the flow volume of the inert gas is set to
exceed 400 litters/min, the accommodating portion 221 may be too
cooled to volatilize the dopant.
[0283] Next, while rotating the crucible 31 in advance, the lower
end of the outer tube 21 is immersed in the melt. At this time, the
lower end of the cylindrical portion 222 of the inner tube 22 is
set so as not to touch the melt.
[0284] Further, as shown in FIG. 15, the doping device 2 is rotated
around the central axis of the outer tube 21 in a direction
opposite to the rotary direction of the crucible 31. In FIG. 15, an
arrow Y1 indicates the rotary direction of the crucible 31, whereas
an arrow Y2 indicates the rotary direction of the doping device
2.
[0285] The dopant placed inside the accommodating portion 221 of
the doping device 2 is gradually sublimated by the heat from the
melt, such that the dopant in a gas form is ejected from the
cylindrical portion 222 of the doping device 2.
[0286] By rotating the doping device 2 and the crucible 31, the
melt outside the outer tube 21 collides with the vane 213 provided
on the outer tube 21 to be introduced into the outer tube 21
through the through-hole 212C as shown in an arrow Y3 in FIG. 15.
The melt inside the outer tube 21 is gradually ejected from the
lower side of the outer tube 21 to form a flow in a direction of an
arrow Y4 shown in FIG. 13. In other words, the melt surface on
which the gas ejected from the cylindrical portion 222 of the inner
tube 22 is stirred, so that the gas is always blown on a new melt
surface. Further, the melt in which the gas is dissolved is ejected
from the opening on the lower end of the outer tube 21.
[0287] A temperature of the melt in the crucible 31 at the time of
doping is set to be in a range from a melting point of a material
of the melt to a point 60.degree. C. above the melting point. In
the present embodiment, since the material of the melt is silicon,
the temperature of the melt is set to be in a range of 1412.degree.
C. or higher and 1472.degree. C. or lower.
[0288] When the gas is dissolved in the melt, the pull-up portion
33 of the pull-up device 1 is detached from the doping device 2 and
mounted with the seed crystal. Then, the pulling-up of the grown
crystal is started.
[0289] According to the present embodiment, following effects can
be obtained.
[0290] (4-1) The doping device 2 is provided with the outer tube 21
having the through-hole 212C at the portion immersed in the melt.
Further, the doping device 2 and the crucible 31 are reversely
rotated with each other when the melt is doped. By rotating the
doping device 2 and the crucible 31, the melt outside the outer
tube 21 collides with the vane 213 provided on the outer tube 21 to
be introduced into the outer tube 21 through the through-hole 212C
to be subjected to the blow of the dopant gas. Then, the melt
having been subjected to the blow of the gas is gradually
discharged from the opening on the lower end of the outer tube
21.
[0291] Since the new melt is always introduced to the portion
within the outer tube 21 at which the gas is blown from the inner
tube 22, the absorption efficiency of the dopant gas can be
enhanced.
[0292] (4-2) Since the absorption efficiency of the dopant gas can
be enhanced only by rotating the doping device 2 and the crucible
31, the absorption efficiency of the dopant gas can be easily
enhanced.
[0293] (4-3) Further, since the melt in which the dopant gas is
dissolved is discharged from the opening on the lower end of the
outer tube 21, the gas containing the dopant no more exists on the
surface of the melt, so that the evaporation of the dopant from the
melt can be restrained, thus further enhancing the doping
efficiency.
[0294] (4-4) The shield 34 is provided on the pull-up device 1 so
that the shield 34 surrounds the doping device 2 to cover the melt
surface. In addition, the doping device 2 includes a heat-shielding
plate 231 that shields transmission of heat ray from the melt. The
heat-shielding plate 231 is disposed to cover a lower side of the
accommodating portion 221 that accommodates the dopant.
[0295] Accordingly, the shield 34 and the heat-shielding plate 231
reliably prevent the transfer of the radiant heat of the melt to
the accommodating portion 221, so that the volatilization rate of
the dopant within the accommodating portion 221 can be lowered as
compared with the volatilization rate in a traditional doping
device.
[0296] Thus, the dopant is not instantaneously volatilized and the
blowing pressure of the dopant gas to the melt can be lowered. In
this exemplary embodiment, the flow volume of the dopant gas
ejected from the doping device 2 to be blown to the melt is
controlled in the range from 3 litters/min to 15 litters/min, the
melt is not blown off when the gas is blown onto the melt.
[0297] Accordingly, since it can be prevented that time allowance
for dissolving the dopant into the melt is lost on account of
excessively ejected dopant gas, the dopant can be sufficiently
dissolved into the melt, so that absorption rate is not
deteriorated. Further, it can be prevented that the formation of
monocrystal is hindered by the blown-off silicon to make it
difficult to manufacture semiconductor wafers having a desired
resistance value.
[0298] (4-5) The doping device 2 is provided with the cylindrical
portion 222 having an upper end in communication with the
accommodating portion 221 to guide the volatilized dopant gas to
the melt. Since the cylindrical portion 222 is provided, the
volatilized dopant gas can be reliably guided to the melt, so that
the doping efficiency to the melt can be enhanced.
[0299] (4-6) Further, the doping device 2 of the exemplary
embodiment includes the cylindrical outer tube 21 that has an
opening on the lower end surface and accommodates the inner tube 22
having the accommodating portion 221 and the cylindrical portion
222. When the inert gas is flowed from the upper side of the melt
to the surface of the melt in doping the melt, since the doping
device 2 includes the outer tube 21 that houses the inner tube 22,
the inert gas is not directly blown to the inner tube 22.
Accordingly, it can be avoided that the inner tube 22 is cooled by
the inert gas to be lower than the evaporation temperature of the
dopant.
[0300] (4-7) In this exemplary embodiment, the lower end of the
outer tube 21 of the doping device 2 is projected toward the melt
relative to the lower end of the cylindrical portion 222 of the
inner tube 22 so that only the lower end of the outer tube 21 is
immersed in the melt to dope the melt.
[0301] Even when a part of the gas ejected from the cylindrical
portion 222 of the inner tube 22 is not dissolved into the melt,
the gas resides within a space defined by the cylindrical portion
222 of the inner tube 22, the outer tube 21 and the heat-shielding
plate 231 without being ejected outside the doping device 2, so
that the doping efficiency can be enhanced.
[0302] (4-8) When the melt is doped, only the lower end of the
outer tube 21 is immersed in the melt without immersing the lower
end of the cylindrical portion 222 of the inner tube 22, the heat
of the melt is not directly transferred to the inner tube 22.
Accordingly, the temperature of the accommodating portion 221 is
not raised on account of the heat of the melt directly transferred
to the inner tube 22. Thus, the increase in the volatilization rate
of the dopant in the accommodating portion 221 can be avoided.
[0303] (4-9) In this exemplary embodiment, the plurality of
heat-shielding plates 231 disposed between the outer tube 21 and
the inner tube 22 and covering the lower side of the accommodating
portion 221 of the inner tube 22 are provided. Accordingly, the
heat ray from the melt can be reliably shielded and the
volatilization rate of the dopant in the accommodating portion 221
can be lowered.
[0304] (4-10) Since the heat-shielding plate 231 (231B) closest to
the accommodating portion 221 of the inner tube 22 of the doping
device 2 is made of a material having relatively high heat
conductivity such as opaque quartz, the heat is not accumulated in
the heat-shielding plate 231B closest to the accommodating portion
221. Accordingly, since the accommodating portion 221 is not heated
by the heat accumulated in the heat-shielding plate 231B, the
volatilization rate of the dopant in the accommodating portion 221
is not accelerated by the presence of the heat-shielding plate
231B.
[0305] Further, since the heat-shielding plate 231A closest to the
melt is made of a material having relatively low heat conductivity
such as carbon heat-insulating material, the heat transmission from
the melt can be blocked at a position remote from the accommodating
portion 221, which also contributes to prevention of increase in
the volatilization rate of the dopant in the accommodating portion
221.
[0306] (4-11) Since the plurality of heat-shielding plates 231 are
spaced apart by a predetermined gap, the heat is not easily
accumulated in the respective heat-shielding plates 231 as compared
with an arrangement in which the heat-shielding plates are
superposed.
[0307] (4-12) In this exemplary embodiment, the temperature of the
melt when being doped is set at the melting point of silicon or
higher and 60.degree. C. above the melting point of silicon or
lower.
[0308] When the temperature of the melt is lower than the melting
point of silicon, in the event that the melt temperature is low
during the doping process, the surface of the melt may be
solidified as a result of lowered silicon temperature when the
doping tube is immersed or the gas is blown, so that the gas is not
easily absorbed.
[0309] On the other hand, when the melt temperature exceeds the
point 60.degree. C. above the melting point, the melt may be
boiled. Further, when the melt temperature exceeds the point
60.degree. C. above the melting point, evaporation of the dopant
gas absorbed in the melt may be promoted to lower the dopant
absorption efficiency.
[0310] Since the temperature of the melt is set at the melting
point of silicon or higher and 60.degree. C. above the melting
point or lower in this exemplary embodiment, the above problems can
be avoided.
[0311] (4-13) When the pressure inside the chamber 30 is 5332 Pa
(converted value of 40 Torr) during the doping process, the dopant
dissolved in the melt may be easily volatilized.
[0312] On the other hand, when the pressure inside the chamber 30
exceeds 79980 Pa (converted value of 600 Torr), though
volatilization of the dopant from the melt can be restrained, high
pressure resistance is required for the chamber 30, which incurs
additional production cost.
[0313] In this exemplary embodiment, since the pressure of the
inert gas is set in a range from 5332 Pa (converted value of 40
Torr) to 79980 Pa (converted value of 600 Torr) during the doping
process, the above problem does not occur.
[0314] (4-14) The flow volume of the inert gas flowing from above
to below the accommodating portion 221 of the doping device 2 is
set at in a range from 50 litters/min to 400 litters/min.
Accordingly, the accommodating portion 221 can be cooled by the
inert gas, thus allowing adjustment of the volatilization rate of
the dopant in the accommodating portion 221.
[0315] (4-15) Since the diameter of the ejecting opening of the gas
on the second cylindrical portion 222B of the inner tube 22 is 20
mm or more, when the flow volume of the dopant gas is set in a
range from 3 litters/min to 15 litters/min, the volatilized dopant
gas is not vigorously blown onto the melt, so that blow-off of the
melt can be reliably avoided.
[0316] (4-16) If the position of the dopant is located very close
to the surface of the melt when being doped, the dopant is disposed
in a high temperature atmosphere due to the heat of the melt, so
that it may become difficult to control the volatilization rate of
the dopant.
[0317] In this exemplary embodiment, since the position of the
dopant is located 300 mm or more above the surface of the melt, the
volatilization rate of the dopant can be reliably controlled.
Modification(s) of Fourth Embodiment
[0318] The present invention is not limited to the above-described
embodiments but may include modifications and improvements made
within a scope where an object of the present invention can be
achieved.
[0319] For instance, the doping device 2 in the fourth exemplary
embodiment includes the outer tube 21 and the inner tube 22, the
outer tube may not be provided.
[0320] As shown in FIG. 16, the doping device 4 having an inner
tube 42 may be used. The doping device 4 includes the inner tube
42, the heat-shielding member 23 and a blow prevention plate 44.
The blow prevention plate 44 prevents the inert gas flowing in the
chamber 30 from directly touching the accommodating portion 221 of
the inner tube.
[0321] The inner tube 42 includes the accommodating portion 221 and
a cylindrical portion 422 (tube portion). The cylindrical portion
422 includes a first cylindrical portion 222A and a second
cylindrical portion 422B. The second cylindrical portion 422B is
provided with through-holes 442B1. Vanes 213 are provided adjacent
to the through-holes 442B1.
[0322] When the melt is doped using the doping device 4, the
through-holes 442B1 and the vanes 213 are immersed into the melt
and the doping device 4 and the crucible are rotated.
[0323] With the use of such doping device 4, since the outer tube
is no longer necessary, the number of the components can be
reduced.
[0324] Though the doping device 2 of the fourth exemplary
embodiment includes the heat-shielding plates 231 covering the
lower side of the accommodating portion 221 of the inner tube 22,
the doping device may alternatively be provided with a
heat-shielding member covering the lateral portion 221C as well as
the lower side of the accommodating portion 221. For instance, a
heat-insulating material may be wound on the lateral portion 221C
and the bottom portion 221B of the accommodating portion 221. With
this arrangement, the transmission of the radiant heat from the
melt to the accommodating portion 221 can be further reliably
prevented.
[0325] Though the doping device 2 of the fourth exemplary
embodiment includes the heat-shielding member 23, the
heat-shielding member may not be provided.
[0326] Though the doping device 2 is rotated to form the flow in
the arrow Y4 shown in FIG. 13 to enhance the doping efficiency when
the melt is doped in the fourth exemplary embodiment, a doping
device 5 having no vanes may be vertically driven (in a direction
of an arrow Y5) to stir the melt as shown in FIG. 17. The doping
device 5 is the same as the doping device 2 of the fourth exemplary
embodiment except that a horizontally protruding vanes 513 are
provided above the through-holes 212C.
[0327] By vertically driving the doping device 5, the melt can be
stirred by the vanes 513 and the temperature of the accommodating
portion 221 of the inner tube 22 can be adjusted to control the
sublimation rate of the dopant.
[0328] Though both of the doping device 2 and the crucible 31 are
reversely rotated in the fourth exemplary embodiment when the melt
is doped, only one of the doping device 2 and the crucible 31 may
be rotated. Incidentally, when the crucible 31 is rotated while the
doping device 2 is fixed, the vanes 213 of the doping device 2 are
preferably provided on a front end in a rotary direction of the
crucible 31 relative to the through-holes 212C.
[0329] Though the lower end of the outer tube 21 of the doping
devices 2 protrudes relative to the lower end of the inner tube 22
in the fourth exemplary embodiment, the lower end of the inner tube
22 and the lower end of the outer tube may be situated at the same
level relative to the melt.
[0330] Though the doping device 2 of the fourth exemplary
embodiment includes the heat-shielding plates 231 covering the
lower side of the accommodating portion 221 of the inner tube 22,
the doping device may alternatively be provided with a
heat-shielding member covering the lateral portion 221C as well as
the lower side of the accommodating portion 221. For instance, a
heat-insulating material may be wound on the lateral portion 221C
and the bottom portion 221B of the accommodating portion 221. With
this arrangement, the transmission of the radiant heat from the
melt to the accommodating portion 221 can be further reliably
prevented.
Fifth Embodiment
[0331] A fifth exemplary embodiment will be described below with
reference to FIGS. 1 and 2.
[0332] FIG. 1 shows a pull-up device of this exemplary embodiment.
FIG. 2 shows a cross-sectional view showing a doping device of the
pull-up device.
[0333] The pull-up device 1 includes a pull-up device body 3 and a
doping device 2.
[0334] The pull-up device body 3 includes a chamber 30, a crucible
31 disposed inside the chamber 30, a heater 32 for heating the
crucible 31 by heat radiation, a pull-up portion 33, a shield 34
and a heat insulating cylinder 35.
[0335] Inert gas such as argon gas is injected into the chamber 30
from above to below. The pressure inside the chamber 30 is
adjustable. During the doping process, the pressure of the inert
gas is set in a range from 5332 Pa (converted value of 40 Torr) to
79980 Pa (converted value of 600 Torr).
[0336] The crucible 31 melts semiconductor wafer material in the
form of polycrystal silicon to prepare a silicon melt. The crucible
31 includes a bottomed cylindrical first crucible 311 made of
quartz and a graphite second crucible 312 disposed outside the
first crucible 311 to accommodate the first crucible 311. The
crucible 31 is supported by a support shaft 36 rotated at a
predetermined speed.
[0337] The heater 32, which is disposed outside the crucible 31,
heats the crucible 31 so as to melt the silicon therein.
[0338] The pull-up portion 33, which is disposed above the crucible
31, is mounted with a seed crystal or the doping device 2. The
pull-up portion 33 is rotatable.
[0339] The heat insulating cylinder 35 is disposed so as to
surround the crucible 31 and the heater 32.
[0340] The shield 34 is a heat-blocking shield for blocking radiant
heat radiated from the heater 32 toward the doping device 2. The
shield 34 surrounds the doping device 2 and covers a surface of the
melt. The shield 34 is configured as a truncated cone having
smaller opening at a lower side than an opening on an upper
side.
[0341] The doping device 2 is a device for volatilizing a solid
dopant and doping the volatilized dopant on the silicon melt in the
crucible 31.
[0342] The dopant may be, for instance, red phosphorus, arsenic and
the like.
[0343] The doping device 2 includes an outer tube 21, an inner tube
22 disposed inside the outer tube 21 and a heat-shielding member
23.
[0344] The outer tube 21, which is bottomed-cylindrical with its
lower end being opened while its upper end being closed, includes
an upper portion 211 for providing an upper end surface and a
lateral portion 212 that extends downwardly from an outer periphery
of the upper portion 211. In the exemplary embodiment, the lateral
portion 212 of the outer tube 21 is configured as a cylinder. The
material of the outer tube 21 is, for instance, transparent
quartz.
[0345] A height T of the outer tube 21 is, for instance, 450 mm. A
diameter R of the lateral portion 212 of the outer tube 21 is
preferably 100 mm or more and 1.3 times as large as a pull-up
crystal diameter or smaller.
[0346] The upper portion 211 of the outer tube 21 is provided with
a support 24 that protrudes upwardly from the upper portion 211.By
mounting the support 24 on the pull-up portion 33 of the pull-up
device 1, the outer tube 21 is held by the pull-up device 1.
[0347] The upper portion 211 of the outer tube 21 covers a
later-described accommodating portion 221 of the inner tube 22 from
the above. The upper portion 211 serves as a blow prevention member
for preventing the above-mentioned inert gas that flows from top to
bottom inside the chamber 30 (in other words, from top to bottom of
the accommodating portion 221) from being directly blown against
the accommodating portion 221.
[0348] The inner tube 22 includes an accommodating portion 221 and
a cylindrical portion 222 connected to the accommodating portion
221 to be in communication therewith.
[0349] The material of the inner tube 22 is, for instance,
transparent quartz.
[0350] The accommodating portion 221, which accommodates solid
dopant, is a hollow columnar portion. The accommodating portion 221
includes a substantially plane-circular upper portion 221A, a
bottom portion 221B disposed to face the upper portion 221A, a
lateral portion 221C disposed between outer peripheries of the
upper portion 221A and the bottom portion 221B.
[0351] The center of the bottom portion 221B is provided with an
opening. Solid dopant is placed on the bottom portion 221B around
the opening. When the solid dopant is volatilized, the dopant gas
is ejected through the opening. A circumference of the opening is
provided with a drop preventing wall 221B1 for preventing the solid
dopant from being dropped.
[0352] The dopant accommodated in the accommodating portion 221 is
preferably positioned at a position where its temperature
approaches the sublimation temperature of the dopant because, when
the accommodating portion 221 is close to the melt, high
temperature therefrom deteriorates thermal insulating effects. In
this embodiment, the dopant is exemplarily placed approximately 300
mm away from the surface of the melt.
[0353] The lateral portion 221C is provided with a support piece(s)
221C1 that is substantially T-shaped in cross section, the support
piece(s) 221C1 protruding outwardly from the accommodating portion
221.By placing the support piece(s) 221C1 on a support(s) 212A
formed on an inner circumference of the outer tube 21, the inner
tube 22 is supported by the outer tube 21.
[0354] The cylindrical portion 222 is a cylindrical member having
open upper and lower end surfaces. An upper end of the cylindrical
portion 222 is connected to the opening on the bottom portion 221B
of the accommodating portion 221.
[0355] A diameter of the cylindrical portion 222 is smaller than
that of the outer tube 21, so that a gap is formed between an outer
circumference of the cylindrical portion 222 and an inner
circumference of the outer tube 21.
[0356] In the present embodiment, the cylindrical portion 222
includes a first cylindrical portion 222A connected to the opening
of the accommodating portion 221 and a second cylindrical portion
222B connected to the first cylindrical portion 222A to extend
downwardly therefrom.
[0357] The first cylindrical portion 222A is integrated with the
accommodating portion 221 while being provided as a body
independent of the second cylindrical portion 222B.
[0358] The first cylindrical portion 222A is provided with a
plurality of ring-shaped grooves 222A1 formed along a
circumferential direction of the first cylindrical portion 222A. In
the present embodiment, three grooves 222A1 are formed. The grooves
222A1 serve to support later-described heat-shielding plates 231 of
the heat-shielding member 23.
[0359] The second cylindrical portion 222B has a diameter of 20 mm
or more and 150 mm or less. Since the second cylindrical portion
222B in the present embodiment is a cylindrical member, its opening
for ejecting the dopant gas also has a diameter in the range from
20 mm to 150 mm. When the outer tube 21 holds the inner tube 22, a
lower distal end of the outer tube 21 protrudes further downward
(toward the melt) than a lower distal end of the second cylindrical
portion 222B.
[0360] The heat-shielding member 23 covers the lower side of the
accommodating portion 221 to block the radiant heat from the melt.
The heat-shielding member 23 has a plurality (exemplarily, five) of
substantially plane-circular heat-shielding plates 231.
[0361] The number of the heat-shielding plates 231 may be
determined in any suitable manner so that the flow rate of the
dopant gas blown onto the melt becomes 3 to 15 L/min. The flow rate
of the gas flowing out of the lower end of the cylindrical portion
222 is larger than the flow rate of the evaporant evaporating from
the melt.
[0362] The sublimation rate of the dopant housed in the
accommodating portion 221 is 10 to 50 g/min.
[0363] The outer diameter of the heat-shielding plates 231 is
substantially equal to the inner diameter of the outer tube 21. The
centers of the heat-shielding plates 231 are provided with holes
2311 into which the cylindrical portion 222 is inserted. The
heat-shielding plates 231 are substantially horizontally disposed
to shield the gap between the cylindrical portion 222 of the inner
tube 22 and the outer tube 21 and to be substantially parallel to
one another.
[0364] In the present embodiment, among the five heat-shielding
plates 231, heat-shielding plates 231A disposed adjacently to the
melt may be made of, for example, carbon heat-insulating material.
The carbon heat-insulating material is formed by impregnating a
material such as a thermoplastic resin with carbon fibers, curing
the material by heating and burning the material under vacuum or
under an atmosphere of inert gas. For heat conductivity of the
heat-shielding plates 231A, a material whose heat conductivity is
20 W/m.degree. C. at 1412.degree. C. may be exemplarily used.
[0365] Among the five heat-shielding plates 231, three
heat-shielding plates 231B disposed adjacently to the accommodating
portion 221 maybe made of opaque quartz. Opaque quartz is formed
by, for example, impregnating quartz glass with multiple fine
bubbles. For heat conductivity of the heat-shielding plates 231B, a
material whose heat conductivity is 8 W/m.degree. C. at
1412.degree. C. may be exemplarily used.
[0366] The plurality of heat-shielding plates 231 are disposed in
the order of the two heat-shielding plates 231A and the three
heat-shielding plates 231B from the lower end of the cylindrical
portion 222.
[0367] The heat-shielding plates 231A are supported by the outer
tube 21 such that projections 212B formed on inner sides of the
outer tube 21 support the outer peripheries of the heat-shielding
plates 231A. A heat-shielding plate 231A (231A1) that is the
closest to the melt is disposed, for example, approximately 80 mm
above the lower distal end of the cylindrical portion 222.
[0368] A heat-shielding plate 231A2 above the heat-shielding plate
231A1 is disposed, for example, approximately 170 mm above the
lower distal end of the cylindrical portion 222. Hence, a gap of
approximately 90 mm is formed between the heat-shielding plate
231A1 and the heat-shielding plate 231A2.
[0369] On the other hand, the heat-shielding plates 231B are
supported by the inner tube 22 such that the peripheries of the
holes 2311 are supported by the grooves 222A1 of the first
cylindrical portion 222A of the cylindrical portion 222 of the
inner tube 22.
[0370] Among the three heat-shielding plates 231B, a heat-shielding
plate 231B1 that is the closest to the melt is disposed, for
example, approximately 250 mm above the lower distal end of the
cylindrical portion 222.
[0371] A heat-shielding plate 231B2 above the heat-shielding plate
231B1 is disposed, for example, approximately 10 mm above the
heat-shielding plate 231B1.
[0372] A heat-shielding plate 231B3 further above the
heat-shielding plate 231B1 is disposed, for example, approximately
10 mm above the heat-shielding plate 231B2. In other words, gaps of
a predetermined size are formed between the heat-shielding plates
231B.
[0373] The distance between the heat-shielding plate 231B1 and the
accommodating portion 221 is exemplarily 30 mm.
[0374] Thus arranged doping device 2 is assembled as follows.
[0375] Initially, solid dopant is inserted into the accommodating
portion 221 of the inner tube 22.
[0376] Next, the heat-shielding plate 231B is attached to the first
cylindrical portion 222A of the cylindrical portion 222 integrated
with the accommodating portion 221. Specifically, the first
cylindrical portion 222A is inserted to the central hole 2311 of
the respective heat-shielding plates 231A and the peripheries of
the holes 2311 of the heat-shielding plates 231B are engaged with
the respective grooves 222A1 of the first cylindrical portion
222A.
[0377] Subsequently, the first cylindrical portion 222A and the
heat-shielding plates 231B are inserted into the outer tube 21 and
the support piece 221C of the accommodating portion 221 is placed
on the support 212A provided on the outer tube 21.
[0378] Next, the heat-shielding plates 231A are inserted into the
outer tube 21 and the outer circumference of the heat-shielding
plates 231A is supported by the projections 212B of the outer tube
21.
[0379] Finally, the second cylindrical portion 222B of the
cylindrical portion 222 of the inner tube 22 is inserted into the
outer tube 21. Specifically, the second cylindrical portion 222B is
inserted into the holes 2311 provided at the center of the
heat-shielding plates 231A supported by the outer tube 21. Then,
the upper end of the second cylindrical portion 222B and the lower
end of the first cylindrical portion 222A are connected.
[0380] The doping device 2 is assembled as described above.
[0381] When using the assembled doping device 2, the support 24
provided on the outer tube 21 of the doping device 2 is attached to
the pull-up portion 33 of the pull-up device 1.
[0382] Inert gas is subsequently flowed from an upper side of the
pull-up device 1 toward the melt. The inert gas flows along the
surface of the melt.
[0383] The inert gas is continuously flowed during conducting the
doping and pulling up a grown crystal. The flow rate of the inert
gas is set to be in a range of in a range from 50 litters/min to
400 litters/min. When the flow volume of the inert gas is set to
exceed 400 litters/min, the accommodating portion 221 may be too
cooled to volatilize the dopant or that the sublimated dopant may
be solidified and adhered.
[0384] Next, the lower end of the outer tube 21 is immersed in the
melt. At this time, the lower end of the cylindrical portion 222 of
the inner tube 22 is set so as not to touch the melt.
[0385] The dopant placed inside the accommodating portion 221 of
the doping device 2 is gradually sublimated by the heat from the
melt, such that the dopant in a gas form is ejected from the
cylindrical portion 222 of the doping device 2 to be dissolved in
the melt.
[0386] A temperature of the melt in the crucible 31 at the time of
doping is set in a range from a melting point of a material of the
melt to a point 60.degree. C. above the melting point. In the
present embodiment, since the material of the melt is silicon, the
temperature of the melt is set to be in a range from 1412.degree.
C. to 1472.degree. C.
[0387] When the gas is dissolved in the melt, the pull-up portion
33 of the pull-up device 1 is detached from the doping device 2 and
mounted with the seed crystal. Then, the pulling-up of the grown
crystal is started.
[0388] According to the present embodiment, following effects can
be obtained.
[0389] (5-1) The shield 34 is provided on the pull-up device 1 so
that the shield 34 surrounds the doping device 2 to cover the melt
surface. In addition, the doping device 2 includes a heat-shielding
plate 231 that shields transmission of heat ray from the melt. The
heat-shielding plate 231 is disposed to cover a lower side of the
accommodating portion 221 that accommodates the dopant.
[0390] Accordingly, the shield 34 and the heat-shielding plate 231
reliably prevent the transfer of the radiant heat of the melt to
the accommodating portion 221, so that the volatilization rate of
the dopant within the accommodating portion 221 can be lowered as
compared with the volatilization rate in a traditional doping
device.
[0391] Thus, the dopant is not instantaneously volatilized and the
blowing pressure of the dopant gas to the melt can be lowered. In
this exemplary embodiment, the flow volume of the dopant gas
ejected from the doping device 2 to be blown to the melt is
controlled at 3 litters/min or more and 15 litters/min or less, the
melt is not blown off when the gas is blown onto the melt.
[0392] Accordingly, since it can be prevented that time allowance
for dissolving the dopant into the melt is lost on account of
excessively ejected dopant gas, the dopant can be sufficiently
dissolved into the melt, so that absorption rate is not
deteriorated. Further, it can be prevented that the formation of
monocrystal is hindered by the blown-off silicon to make it
difficult to manufacture semiconductor wafers having a desired
resistance value.
[0393] (5-2) The doping device 2 is provided with the cylindrical
portion 222 having an upper end in communication with the
accommodating portion 221 to guide the dopant gas to the melt.
Since the cylindrical portion 222 is provided, the volatilized
dopant gas can be reliably guided to the melt, so that the doping
efficiency to the melt can be enhanced.
[0394] (5-3) Further, the doping device 2 of the exemplary
embodiment includes the cylindrical outer tube 21 that has an
opening on the lower end surface and accommodates the inner tube 22
having the accommodating portion 221 and the cylindrical portion
222. When the inert gas is flowed from the upper side of the melt
to the surface of the melt in doping the melt, since the doping
device 2 includes the outer tube 21 that houses the inner tube 22,
the inert gas is not directly blown to the inner tube 22.
Accordingly, it can be avoided that the inner tube 22 is cooled by
the inert gas to be lower than the evaporation temperature of the
dopant.
[0395] (5-4) In this exemplary embodiment, the plurality of
heat-shielding plates 231 disposed between the outer tube 21 and
the inner tube 22 and covering the lower side of the accommodating
portion 221 of the inner tube 22 are provided. Accordingly, the
heat ray from the melt can be reliably shielded and the
volatilization rate of the dopant in the accommodating portion 221
can be lowered.
[0396] (5-5) Since the heat-shielding plate 231 (231B) closest to
the accommodating portion 221 of the inner tube 22 of the doping
device 2 is made of a material having high heat conductivity such
as opaque quartz, the heat is not accumulated in the heat-shielding
plate 231B closest to the accommodating portion 221. Accordingly,
since the accommodating portion 221 is not heated by the heat
accumulated in the heat-shielding plate 231B, the volatilization
rate of the dopant in the accommodating portion 221 is not
accelerated by the presence of the heat-shielding plate 231B.
[0397] Further, since the heat-shielding plate 231A closest to the
melt is made of a material having relatively low heat conductivity
such as carbon heat-insulating material, the heat transmission from
the melt can be blocked at a position remote from the accommodating
portion 221, which also contributes to prevention of increase in
the volatilization rate of the dopant in the accommodating portion
221.
[0398] (5-6) Since the plurality of heat-shielding plates 231 are
spaced apart by a predetermined gap, the heat is not easily
accumulated in the respective heat-shielding plates 231 as compared
with an arrangement in which the heat-shielding plates are
superposed.
[0399] (5-7) In this exemplary embodiment, the temperature of the
melt when being doped is set in the range from the melting point of
silicon to the point 60.degree. C. above the melting point of
silicon.
[0400] When the temperature of the melt is lower than the melting
point of silicon, the dopant gas absorption may be hindered. On the
other hand, when the melt temperature exceeds the point 60.degree.
C. above the melting point, the melt may be boiled. Further, when
the melt temperature exceeds the point 60.degree. C. above the
melting point, evaporation of the dopant gas absorbed in the melt
may be promoted to lower the dopant absorption efficiency.
[0401] Since the temperature of the melt is set at the melting
point of silicon or higher and 60.degree. C. above the melting
point or lower in this exemplary embodiment, the above problems can
be avoided.
[0402] (5-8) When the pressure inside the chamber 30 is 5332 Pa
(converted value of 40 Torr) during the doping process, the dopant
dissolved in the melt may be easily volatilized.
[0403] On the other hand, when the pressure inside the chamber 30
exceeds 79980 Pa (converted value of 600 Torr), though
volatilization of the dopant from the melt can be restrained, high
pressure resistance and heat resistance are required for the
chamber, which incurs additional production cost.
[0404] In the exemplary embodiment, since the pressure inside the
chamber 30 when being doped is set within the above range, the
above problem can be avoided.
[0405] (5-9) The flow volume of the inert gas flowing from above to
below the accommodating portion 221 of the doping device 2 is set
at in a range from 50 litters/min to 400 litters/min. Accordingly,
the accommodating portion 221 can be cooled by the inert gas, thus
allowing adjustment of the volatilization rate of the dopant in the
accommodating portion 221.
[0406] (5-10) Since the diameter of the ejecting opening of the gas
on the second cylindrical portion 222B of the inner tube 22 is 20
mm or more, when the flow volume of the dopant gas is set in a
range from 3 litters/min to 15 litters/min, the volatilized dopant
gas is not vigorously blown onto the melt, so that blow-off of the
melt can be reliably avoided.
[0407] (5-11) If the position of the dopant is located very close
to the surface of the melt when being doped, the dopant is disposed
in a high temperature atmosphere due to the heat of the melt, so
that it may become difficult to control the volatilization rate of
the dopant.
[0408] In this exemplary embodiment, since the position of the
dopant is located 300 mm or more above the surface of the melt, the
volatilization rate of the dopant can be reliably controlled.
Sixth Embodiment
[0409] Next, a sixth exemplary embodiment will be described below
with reference to FIG. 19. In the following description, the same
components as those having been explained above will be referenced
with the same numeral to omit the description thereof.
[0410] A doping device 5 of this exemplary embodiment has the same
inner tube 22, support 24 and heat-shielding member 23 as the fifth
exemplary embodiment, an outer tube 51 and a tube 55 disposed
between the outer tube 51 and the inner tube 22.
[0411] The outer tube 51 has approximately the same structure as
the outer tube 21 of the fifth exemplary embodiment except that a
plurality of projections 512A extending toward the inside of the
outer tube 51 are provided on an inside of the lower end of the
outer tube 51. The other arrangement of the outer tube 51 is the
same as the outer tube 21 of the fifth exemplary embodiment.
[0412] The tube 55 has open upper end and lower end and has a
diameter smaller than the outer tube 51 and greater than the
cylindrical portion 222 of the inner tube 22. The tube 55 is
disposed on the projections 512A and is located between the outer
tube 51 and the inner tube 22. A gap is provided between the inner
circumference of the lateral portion 212 of the outer tube 51 and
the outer circumference of the tube 55. A gap is also provided
between the inner circumference of the tube 55 and the cylindrical
portion 222 of the inner tube 22.
[0413] The height of the tube 55 is smaller than a distance from
the lower end of the outer tube 51 to the heat-shielding plate 231A
(231A1) closest to the melt, so that a gap is provided between the
tube 55 and the heat-shielding plate 231A (231A1).
[0414] In this exemplary embodiment, the doping device 5 is used to
dope the melt as follows. Incidentally, the pressure in the chamber
30, the flow volume of the inert gas, the temperature of the melt,
the position of the dopant from the melt surface, the flow volume
of the dopant gas blown to the melt and the sublimation rate of the
dopant when the doping process is conducted are the same as those
in the fifth exemplary embodiment.
[0415] The lower end of the tube 55 is immersed in the melt. At
this time, the lower end of the cylindrical portion 222 of the
inner tube 22 and the lower end of the outer tube 51 are set so as
not to touch the melt.
[0416] The dopant placed inside the accommodating portion 221 of
the doping device 5 is gradually sublimated by the heat from the
melt, such that the dopant in a gas form is ejected from the
cylindrical portion 222 of the doping device 5 to be dissolved in
the melt.
[0417] At this time, some of the gas ejected from the cylindrical
portion escapes to the outside of the cylindrical portion 222
without being dissolved in the melt. Further, a part of the gas is
reflected on the surface of the melt without being dissolved in the
melt. The part of gas passes through the gap between the outer
circumference of the lower end of the cylindrical portion 222 and
the inner circumference of the tube 55 to go up, and subsequently
reflected by the heat-shielding plate 231 to be introduced between
the inner circumference of the outer tube 51 and the outer
circumference of the tube 55. Then, the gas is introduced to the
melt surface (see arrow Y5 in FIG. 19).
[0418] In other words, the gap between the outer circumference of
the lower end of the cylindrical portion 222 and the inner
circumference of the tube 55 and the gap between the inner
circumference of the outer tube 51 and the outer circumference of
the tube 55 define a path for introducing the gas to the melt
surface.
[0419] According to this exemplary embodiment, as well as the
effects (5-1) to (5-11) of the fifth exemplary embodiment,
following effects can be obtained.
[0420] (6-1) The doping device 5 includes the tube 55 disposed
between the outer tube 51 and the inner tube 22. A part of the gas
ejected from the cylindrical portion 222 and not dissolved in the
melt passes through the gap between the outer circumference of the
lower end of the cylindrical portion 222 and the inner
circumference of the tube 55, goes up and subsequently is reflected
by the heat-shielding plate 231 to be introduced to the space
between the inner circumference of the outer tube 51 and the outer
circumference of the tube 55. Then, the gas is re-introduced to the
melt surface. Since the gas not dissolved in the melt can be
introduced to the melt surface again, the doping efficiency can be
enhanced.
Modification(s) of Fifth to Sixth Embodiments
[0421] The present invention is not limited to the above-described
embodiments but may include modifications and improvements made
within a scope where an object of the present invention can be
achieved.
[0422] For instance, though the doping devices 2, 5 of the fifth
and sixth exemplary embodiments include the outer tubes 21, 51, the
outer tube may not be provided. For instance, as shown in FIG. 7, a
blow-preventing plate 64 for preventing a blow of the gas to the
accommodating portion 221 of the inner tube 22 maybe provided above
the accommodating portion 221 in place of the outer tube. When the
doping device 6 having no outer tube is used, all of the
heat-shielding plates 231 are preferably fixed on the inner tube
22.
[0423] The radiation of radiant heat of the melt to the
accommodating portion 221 is blocked by the heat-shielding member
23 and the shield 34 in the fifth and sixth exemplary embodiments.
However, a heat-shielding plate 25 may be provided on the lateral
portion 212 of the outer tube 21 of a doping device 2' as shown in
FIG. 20 and the radiation of the radiant heat of the melt to the
accommodating portion 221 may be blocked by the heat-shielding
plate 25, the heat-shielding member 23 and the shield 34.
Incidentally, the doping device 2' shown in FIG. 20 is the same as
the doping device 2 in the fifth exemplary embodiment except for
the provision of the heat-shielding plate 25.
Examples
Examples of First to Third Embodiments
[0424] Next, examples of the first to third exemplary embodiments
will be described below.
[0425] The melt was doped using the same pull-up device as that of
the first exemplary embodiment and a grown crystal was pulled up by
CZ method.
Examples 1 to 6
1. Doping Condition
(1) Doping Device
[0426] An outer tube having a diameter of 150 mm was used. The
diameter of the second cylindrical portion of the inner tube was 20
mm. Five heat-shielding plates were used as the heat-shielding
member, where two graphite heat-shielding plates and three opaque
quartz heat-shielding plates were arranged in this order from the
lower end of the cylindrical portion.
(2) Other Conditions
[0427] The other conditions are shown in Tables 1 and 2.
Incidentally, the melt in the crucible was silicon melt. The dopant
was 300 g of arsenic.
TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Pressure in
Chamber (Pa) 5332 5332 59985 Flow Volume of Ar 50 50 150
(litters/min) Flow Rate in Chamber (m/s) 0.218 0.218 0.058
Temperature of Melt (.degree. C.) 60.degree. C. above the
60.degree. C. above the 60.degree. C. above the melting point of
melting point of melting point of Si (1472) Si (1472) Si (1472)
Dopant Position (from the 300 mm above 300 mm above 300 mm above
Surface of the Melt) Sublimation Rate of Dopant 40 50 30
(g/min)
TABLE-US-00002 TABLE 2 Example 4 Example 5 Example 6 Pressure in
Chamber (Pa) 59985 59985 59985 Flow Volume of Ar 200 200 200
(litters/min) Flow Rate in Chamber (m/s) 0.078 0.078 0.078
Temperature of Melt (.degree. C.) Melt point of 60.degree. C. above
the 30.degree. C. above the Si (1412) melting point of melting
point of Si (1472) Si (1442) Dopant Position (from the 300 mm above
300 mm above 300 mm above Surface of the Melt) Sublimation Rate of
Dopant 10 30 20 (g/min)
<Comparison 1>
[0428] The melt was doped using a doping device having no
heat-shielding plate. The doping device was the same as the doping
device used in the examples 1 to 6 except that the heat-shielding
plate was not provided. The doping conditions are shown in the
following Table 3.
TABLE-US-00003 TABLE 3 Comparison 1 Pressure in Chamber (Pa) 5332
Flow Volume of Ar (litters/min) 50 Flow Rate in Chamber (m/s) 0.218
Temperature of Melt (.degree. C.) 60.degree. C. above the melting
point of Si (1472) Dopant Position (from the Surface 300 mm above
of the Melt) Sublimation Rate of Dopant (g/min) 100
[0429] The grown crystal was pulled up after the doping process was
completed. The pulling-up condition was the same as that in the
examples 1 to 6.
[0430] 2. Results
[0431] In Tables 1 to 3, the flow rate in the chamber (gas flow
rate at the entrance of the chamber) was calculated as:
[0432] V(m/s)=(flow volume (litters/min))*0.001/60*101300/(pressure
in chamber (Pa))/3.14/(radius(m)).sup.2, where radius (m) was based
on a diameter of the chamber entrance of inert gas. The flow rate
of the dopant was calculated based on a diameter of the exit of the
dopant doping tube 222.
[0433] As can be seen in FIG. 11, the relationship between the
sublimation rate and absorption rate shown in the Examples 1 to 6
revealed that the doping efficiency was enhanced and less varied as
the sublimation rate of the dopant was lowered.
[0434] The sublimation rate of the dopant could be restrained at a
low level when the flow rate in the chamber (the gas flow rate at
the entrance of the chamber) was in a range of 0.05 to 0.2 m/s.
When the flow rate in the chamber exceeded 0.2 m/s, the sublimation
rate of the dopant was too increased to conduct a proper doping. It
was confirmed that 10 to 50 g/min of the sublimation rate of dopant
and 0.05 to 0.2 m/s of the flow rate in the chamber were
effective.
[0435] On the other hand, the comparison 1 showed faster
sublimation rate and greater variation of doping efficiency than
the examples 1 to 6.
[0436] Further, after studying the relationship between the
solidification rate and the resistivity for the example 5 and the
comparison 1, it was confirmed that the resistivity was 3.0
m.OMEGA.cm or lower for all solidification rates in the example 5.
In contrast, great variation was found in the comparison 1 and some
of the portions of 0 to 20% solidification rate exhibited
resistivity more than 3.0 m.OMEGA.cm. So, it was confirmed that an
ingot having resistivity of 3.0 mQ.OMEGA.cm or less could not be
constantly manufactured.
[0437] It is conceivable that a large amount of the dopant is added
without using the injecting method according to the first to the
third exemplary embodiments for the purpose of producing
low-resistive crystal. However, when a large amount of dopant is
doped, it is difficult to form a monocrystal and yield rate is
lowered. Further, adding a large amount of dopant in a
low-absorbing adding method results in extremely low efficiency,
unnecessary waste of the dopant, and consequently increase in
production cost. Further, when a large amount of dopant is added,
since a large amount of evaporant is ejected, the evaporant adheres
on an exhaust system of the pull-up device, which requires
increased number of maintenance, thereby considerably deteriorating
the efficiency.
Examples of Fourth Embodiment
[0438] Next, examples of the fourth exemplary embodiment of the
invention will be described below.
[0439] The melt was doped using the same pull-up device as that of
the fourth exemplary embodiment and a grown crystal was pulled up
by CZ method.
Examples 7 to 9
1. Doping Condition
[0440] (1) Doping Device
Example 7
[0441] The doping device 5 having the horizontally provided vanes
513 shown in FIG. 17 was used. The diameter of the outer tube was
150 mm. The diameter of the second cylindrical portion of the inner
tube was 20 mm. Five heat-shielding plates were used as the
heat-shielding member, where two heat-shielding plates made of
carbon heat-insulating material and three opaque quartz
heat-shielding plates were arranged in this order from the lower
end of the cylindrical portion.
Examples 8 and 9
[0442] The doping device shown in FIG. 13 was used. The diameter of
the outer tube and the inner tube and the other arrangement were
the same as the example 7.
[0443] Comparison 2: A conventional doping device with an outer
tube of 100 mm diameter was used. The doping device had no
heat-shielding plate and conducted no tube-immersion.
(2) Other Conditions
[0444] The other conditions of the examples 7 to 9 and the
comparison 2 will be shown in Table 4. Incidentally, the melt in
the crucible was silicon melt. The dopant was 300 g of arsenic. The
crucible and the doping device were reversely rotated.
TABLE-US-00004 TABLE 4 Dopant Amount (g) 300 Flow Volume of Ar
(litters/min) 200 Pressure in Chamber (Pa) 59985 Pressure in
Chamber (Torr) 450 Temperature of Melt (.degree. C.) melting point
of Si (1412) Rotation Speed of Crucible (rpm) 1 Rotation Speed of
Doping Device (rpm) 5 Sublimation Rate (min) 27
<Comparison 2>
[0445] The melt was doped using the doping device of the example 7
having no heat-shielding plate. The doping device was the same as
the doping device used in the example 7 except that the
heat-shielding plate was not provided. The doping condition was the
same as that in the example 7.
[0446] Subsequently, the grown crystal was pulled up after the
doping process was completed. The pulling-up condition was the same
as that in the example 7.
2. Results
[0447] The absorption rate of the dopant in the examples 7 to 9 was
66% or more, which proved that the dopant was absorbed at a high
rate.
[0448] In contrast, the absorption rate of the dopant in the
comparison 2 was barely 54%.
[0449] Further, when temporal dependence of the resistivity of the
top of the pulled-up ingots was compared after doping the melt
according to the methods of the examples 7 to 9 and the comparison
2 as shown in FIG. 18, it was confirmed that the doping efficiency
was enhanced and the resistivity was low in the example 7 as
compared to the comparison 2 because no melt was blown off and the
blowing speed was controlled in the example 7.
Examples of Fifth to Sixth Embodiments
[0450] Next, examples of the fifth and sixth exemplary embodiments
of the invention will be described below. The melt was doped using
the same pull-up device as that of the fifth exemplary embodiment
and a grown crystal was pulled up by CZ method.
Example 10
1. Doping Condition
(1) Doping Device
[0451] The doping device 5 shown in FIG. 19 was used. The diameter
of the outer tube was 150 mm. The diameter of the second
cylindrical portion of the inner tube was 20 mm. Five
heat-shielding plates were used as the heat-shielding member, where
two heat-shielding plates made of carbon heat-insulating material
and three opaque quartz heat-shielding plates were arranged in this
order from the lower end of the cylindrical portion.
(2) Other Conditions
[0452] The other conditions are shown in Table 5. Incidentally, the
melt in the crucible was silicon melt. The dopant was 300 g of
arsenic.
TABLE-US-00005 TABLE 5 Dopant amount (g) 300 Ar flow volume
(litters/min) 50 Pressure in chamber (Pa) 5332 Pressure in chamber
(Torr) 40 Melt temperature (.degree. C.) Melt point of silicon
(1412) + 60
<Comparison 3>
[0453] The melt was doped using the doping device shown in FIG. 2
of which heat-shielding plate was removed. The doping device was
the same as the doping device used in the example 10 except that
the heat-shielding plate is not provided. The doping condition was
the same as the example 10.
[0454] Subsequently, the grown crystal was pulled up after the
doping process was completed. The pulling-up condition was the same
as that in the example 10.
2. Results
[0455] The sublimation rate of dopant was 50 g/min and the flow
volume of the dopant gas ejected from the doping device was 15
litters/min in the example 10. No melt was spattered when the melt
was doped in the example 10.
[0456] In contrast, the sublimation rate of dopant was 100 g/min
and the flow volume of the dopant gas ejected from the doping
device was 25 litters/min in the comparison 3. The melt was
spattered when the melt was doped in the comparison 3.
[0457] It was confirmed that melt spatter could be avoided and
semiconductor wafers having a desired resistance value could be
manufactured in the example 10.
[0458] When temporal dependence of the resistivity of the top of
the pulled-up ingots was compared after doping the melt according
to the methods of the example 10 and the comparison 3 as shown in
FIG. 21, it was confirmed that the doping efficiency was enhanced
and the resistivity was low as compared to the comparison 3 because
no melt was blown off and the blowing speed was controlled in the
example 10. It was also confirmed that the dopant absorption
efficiency of the comparison 3 was 54%, whereas the dopant
absorption efficiency of the example 10 was 62%, showing that the
absorption efficiency was enhanced in the fifth and the sixth
exemplary embodiments.
Industrial Applicability
[0459] The invention can be utilized in an injection method for
injecting a dopant gas into a melt.
* * * * *